Yes it is viable but not with Shield.

Your best bet would to use Mage Armor, since it is a single action spell as opposed to the reaction of Shield that has specifics on when you are allowed to cast it (emphasis mine).

Casting Time: 1 reaction, which you take when you are hit by an attack or targeted by the magic missile spell

So unless you actually have someone hit you repeatedly you can't cast this spell all that often per PHB 196. At least by RAW.

A reaction is an instant response to a trigger of some kind...

This section goes on to say that the opportunity attack is one such instance of a reaction but you can't take it unless something would trigger that as detailed in all the descriptions of reactions. This why when you ready an action you are required to specify a trigger.

Mage Armor could be used as often as necessary to regenerate the ward, unless there is errata somewhere that changes the wording to slots as opposed to level. One thing to note is that spells with verbal components could be overheard and thus could give away position or spoil the element of surprise, so choose when to do this with care.

That is correct

As you have quoted, there is no difference in a spell cast via Ritual or spell slots and both refill the Arcane Ward.

But, it is not as bad balance-wise as you think. You still have the hard cap of (PHB, 115)

The ward has a hit point maximum equal to twice your wizard level + your Intelligence modifier.

This is also confirmed via published Sage Advice

Q: Does casting alarm as a ritual heal Arcane Ward?

A: Any abjuration spell of 1st level or higher cast by an abjurer can restore hit points to his or her Arcane Ward. As is normal for healing, the ward can’t regain more hit points than its hit point maximum: twice the wizard’s level + the wizard’s Intelligence modifier.

But it's not that bad

It'll never pass that and that's okay. This is what the abjuration wizard does! However, as DM, you can always say there isn't enough time to complete the ritual spell (which is 11 minutes.)

Mearls has said this isn't intended

rules as written yes, as intended no