I don't wish to belabour the point, and I'd be very excited to see an Invaders Masterworks line. But seeing as that title has been collected already in a series of trades, mindful of the number of quality titles that remain uncollected in any colour format whatsoever, and considering the small number of open slots between now and Volume 200 (presuming the annual and biannual releases will continue apace), I wouldn't feel secure in betting the mortgage money on that one for Volume 200.
I will take another stab at why the Invaders won't be V200 is that it would be collected in a mere 4 volumes (no x-overs right?). Defenders and Team-Up both have 14 mapped runs each and Captain Marvel a mere 6. I believe that we'll see a new line that will be not only a milestone, but will have a longer run. Which, much to my disappointment means that Strawberry Shortcake is out. Very few fit that bill at this point, Kid Colt, Millie (both of which are longshots IMHO) and some of the more modern titles. There's been lots of buzz on this board about New Mutants, but I am not too hot on the idea of picking up more 80's stuff before Spider-Man, Avengers, FF, etc. get there. I think that even Uncanny is pushing it with one/year at this point considering the material.