Basement – put tile in the basement over Ditra and existing mastic

My basement has been prone to getting water for many years before I bought the house. We're having the basement walls repaired (excavated outside) & sealed. So this problem should go away.

The basement floor currently has linoleum tiles that are all coming up from the years of constant water damage. Beneath them is what looks like a black mastic. Its hardened to the touch in most areas (there are a few sticky sections).

I understand it might have asbestos in it. We had an asbestos inspection done recently and they tested the tiles (report says 0% asbestos) but it is unclear if they tested the mastic. The room is over 1100sqft so it would be alot of work to get it all off the floor and the possibility of asbestos being in it makes removal that much less appealing.

I've read mixed things on the internet about thinset over mastic. I was thinking about laying Ditra over the mastic to accomplish a few things:

1. I can lock the asbestos down, safe beneath the floor
2. I dont have to kill myself trying to remove it
3. Acting as a waterproofing material

My concern is thinset not bonding well to the mastic covered floor. I've read that if I use a high quality thinset, I should be able to secure the Ditra to the mastic pretty well. I'm considering using Laticrete 254 Platinum.

I also wonder if the mastic will hold moisture in the thinset and if so, if I should opt for an unmodified thinset instead (if both mastic and Ditra will be impervious to water).