More feats and maneuvers won't necessarily slow down the game. Optional tactical rules very likely will slow down the game. Since those rules are optional, you can tailor them to the group you are playing with.I agree that limiting options does speed up turns.
On the other hand, I am quite sure that there will be many more options available in the player's handbook and the DMs guide when it is launched. (probably more feats, more maneuvers, optional tactical rules, etc.)
I am interested to find out if using the options will slow down the game.
Also, we haven't really seen the final math for monsters. If ACs and HP go up, we might see a little slow down. How much? Can't tell. Generally, I've been adding HP to the monsters in my sessions and sometimes I give them better armor. If it has slowed down the game, we haven't really noticed.
If you want a story-focused game you can keep the game light, if you want it more combat focused you can pile up on optional rules. 3e or 4e wasn't built in this manner, they just assumed you would run a "default" game.
I think they did a very good move with optional tactical rules. As a DM, I will probably run it on a per-encounter basis. Small random encounters with just the basic rules, while the boss fight with the full tactical rules. Sure I could have house-ruled this in 3e, but I do think this will work out better. (In 4e, I haven't even thought about house ruling the combat rules. They game is so tied to the grid and it's interrupts and all that it would just be too much work).