I hope the TMs and HMs don't change, personally, especially now that the TMs have infinite uses. That was something that I have wanted to see for years, and after getting used to it in Gen 5, it makes it harder for me to use the TMs in previous generations now. So I definitely hope they don't change a thing with how the TMs work now.
As for HMs, even though yes many parts of Europe are landlocked, I can still see them returning and serving the same use as they have always done. They're there for a reason, to serve as puzzle-solvers and to prevent you from going too far ahead in the game early on when you're not supposed to yet (which is why Gens 1-4 had HMs require badges, so you wouldn't trade HM users in and go farther ahead without the badges, though that is null in Gen 5). The games are also largely RPG-like in nature, so obstacles are bound to appear. Even if they outright got rid of the necessities of HMs, which I honestly doubt they will, they will still incorporate some sort of obstacles that you have to figure out how to bypass.
And besides, in regards to Surf, there's still always ponds, small lakes and rivers.