As you saw in the Chat, examples of contemporary re-spelling due to elision are very rare — I believe the only unambiguous examples we came up with were bosun and gunnel, and even those date back to the 19th Century, and do not replace boatswain and gunwale but exist alongside them.
I think it very unlikely that the next century will see any great extension of re-spelling, for elision or any other change in pronunciation. I see three reasons for this:
First: Spelling is and must be inherently conservative — witness the spelling of standard Modern English and Modern French. The purpose of writing is to preserve the integrity of and intelligibility of utterances across both space and time; and when you change spelling you degrade the integrity and raise a barrier to intelligibility between an old-spelling writer and a new-spelling reader. This was recognized by one of our earliest spelling reformers, William Bullokar, who at a time when spelling was much more fluid than it is today wrote of his immediate predecessors:
the vſe of both Ortographies muſt be had during one age, and afterwards (by reaſon of records, euidences, and ſuch like, not to be altered by Printing) the olde muſt not be much ſtrange, but in eaſie vſe, bycauſe neceſſitie alloweth ſuch euidences, &c. with the ſame letters as they now are, which is one of the chiefeſt pointes to be regarded in any amendment of Ortographie, whereof M. Cheſter greatly fayled, as appeareth by his workes printed with his Ortography.
–Bullokars Booke at large, for the Amendment of Orthographie for English ſpeech (1580)
Bullokar wrote at a time when spelling was much more fluid than it is today, and his criticism was specifically directed at the proposals of Thomas Smith and “Mayſter Cheſter” (John Hart, Chester Herald) for new letters— they “left out of their amendment diuers of the letters now in vse, and alſo brought in diuers of new figure and faſhion, hauing no part in figure or faſhion of the old, for whoſe ſoundes they were changed in figure, or newly deuisſed, ſtrange to the eye, and thereby more ſtudie to the memory” — but his point holds true today. Changing the spelling of a single word will at the very least mark an old spelling with a “quaintness” which was no part of the author’s intention, and may make its meaning entirely opaque; wholesale spelling reform cuts succeeding generations off from their cultural heritage. This is the rock on which “rational spelling”, from Thomas Smith to Bernard Shaw, has foundered, and probably always will.
Second: Changes in spelling and changes in pronunciation come from quite different sources. Phonetic evolution is “bottom-up”: a change appears (occasionally at a clearly identifiable place and time, in the idiolect even of a specific individual, but more often “mysteriously”, “spontaneously”) spreads from person to person, from community to community, and eventually establishes itself, globally or regionally, or dies. Orthographic evolution is “top-down”: it is governed in the end not by what the general population write in their letters, journals, blogs and tweets but by a single small and cohesive population of publishers and professional writers. These “speak”, by and large, to each other. They are concerned with lexical and syntactical precision in the written language alone, and only peripherally with pronunciation and prosody; and that peripheral concern is met by specialized technical notation systems like IPA. The movers and shakers at the peak of the written-English pyramid have for the most part no interest to be served by re-spelling.
Third: There is a small population of writers who do have an interest in representing colloquial pronunciation— playwrights, screenwriters, novelists, many journalists. It is these who have developed such “phonetic” and dialect spellings as hafta, gonna, wanna, garridge, nucular, “E sez, sez e,” “Mahty lahk a rose”, “Ah dun bin ruint”. Such writers have no interest in replacing existing spellings with these coinages. On the contrary: their concern is to suggest colloquial pronunciation by means of a handful of phoneticisms, without making it unintelligible to the average reader. Even so conscientious a writer of dialect as Bernard Shaw eventually gave up the effort of through-phoneticization:
THE FLOWERGIRL: Ow, eez ye-ooa san, is e? Wal, fewd dan y’ de-ooty bawmz a mather should, eed now bettern to spawl a pore gel’s flahrzn than ran awy athaht pyin. Will ye-oo py me f’ them? [Here, with apologies, this desperate attempt to represent her dialect without a phonetic alphabet must be abandoned as unintelligible outside London.] –Pygmalion
What these writers require is the situation which now obtains — a repertory of marked dialectal and colloquial forms alongside the standard orthography. I think it very likely that this will continue to be the case for the foreseeable future.
Best Answer
These are all quite old names with many syllables—an ideal place for ellipsis, elision, and contraction.
The -cester bit is from the Old English word ceaster, which in itself is borrowed from Latin castrum. It is thus cognate to castle. (The palatalisation of the initial /k/ to /tʃ/ is common in Old English and was more widespread in some dialects than in others, so at some point, there were probably two variants around: caster /kastər/ and ceaster /tʃastər/.)
In Old English, ceaster referred to a Roman town or settlement (in England). As tchrist notes in his comment, some other places that have this element in their names include Lancaster, Doncaster, and Manchester.
The first part of names that have -cester tend to be inherited place names of either Anglo-Saxon or (even earlier) British Celtic stock, often names of rivers or other local toponyms.
Going from Old English down through the centuries, the cities the first element of whose names ended in a consonant (like Lan-, Don-, Man-) usually kept a fuller version of the word ceaster, retaining the initial consonant. The ones whose first element ended in a vowel, on the other hand, ended up having the initial /tʃ/ (or /k/, as in Lancaster and Doncaster) in an intravocalic position, where it was quite likely to be weakened—something that happens often in place names, especially longer ones.
Thus, Leicester and Gloucester were once pronounced as they’re written, with a /tʃ/ (or perhaps /k/); but that consonant was weakened over time and eventually disappeared altogether, leaving the vowels free to contract into single monophthongs, too.