TMs will be expanded for sure. There's literally no doubt in my mind that the number will increase. They'll probably replace a few TMs with other moves (as they have in the past) but I expect the general list to stay pretty much the same as last generation.
As for HMs, I hate them. I really honestly hate them more than anything. Essentially when planning out a team or just going through the game before you play you have to remember to cover each HM required to beat the game or just for convenience sake (like Fly). I find it ridiculous that pokemon like Wailord or Swellow need to learn Surf / Fly respectively before being able to actually do it. It didn't make much sense to me.
What I would like to see from HMs is this:
1. Keep them, but make them non-permanent. I don't understand why they were ever permanent in the first place.
2. Once you have the HM, you aren't required to teach it to a Pokemon in order for the Pokemon to be able to use it outside of battle. You just need the corresponding badge and the HM, and the Pokemon itself simply has to have the POTENTIAL of being able to learn the move (for example, say you have the Surf HM and its corresponding badge and you have a Swanna. It doesn't have to physically know Surf to be able to Surf outside of battle).
3. You can still teach it to your Pokemon because certain HMs are very useful in battle too (i.e. Surf / Waterfall).
I feel like it's an old mechanic that just needs to be dropped. It's just an inconvenience and I don't believe we'll ever have another HM Slave as good as Bibarel (and most people don't even want him in their team anyway).
I know Black and White took a step in the right direction making it so that the only REQUIRED HM as far as I was concerned was Cut. And you only had to use it once, so you could catch some Purrloin or something early (and extra one if you wanted), teach it Cut, and then forget about it later. They're almost there though and I'm hoping HMs are dropped almost entirely.
I like the idea of having HM's as more of an ability than having to take up a move slot, but I think a more logical way they could enforce this - considering the direction they've gone with gen 5 - is to simply make HM moves replaceable, then for example, you could teach Cut to your Scyther and delete, say, X-Scissor, and then once you're done replace the HM with the TM again seeing as you can use them however many times you want now. This might become a little tedious but it saves the whole move deleter process and also means you're less likely to have to go to the PC and switch your team around just to get past a tree or a boulder etc.