I have gone down the same path as you are about to.
First let me show you my project. This is a 2007 MADP.
This is the passenger slide without the small couch. The slide sits much higher off the floor than you would anticipate. The original couch was designed with the raised floor in mind. Part of the couch will overhang the slide out raised floor. If you intend to use the couch again (or to sell it) you will need to make a set of legs for the rear of the couch to stand level.
I created a entertainment cabinet, with a TV lift, a bar storage area, and an electric fireplace.
I put a couple of electric "theater" chairs across from it.
From my experience working on the non-flat floor slide. I only really see 2 ways to accomplish what you want to do.
First would be to build an extension to the slide out floor (i.e., come further out from the wall). This would allow you to fit a "euro-recliner" with its original base. The downside of this is the slide out would now intrude even further into the aisle with the slide is in.
Second method (what I would do) would be to remove the base from the chair and mount it directly into the slide. This is what the bus conversion companies are doing when they use the OEM Prevost slides (those are not flat floor).
2014 Prevost Millennium H3-45 Quad Slide