I actually doubt that Smash 4 will end up slower than Brawl. As someone who played Brawl (with a random Purple banner for that silly game), I'll expand on why I think Smash 4 will probably end up better:
1. Edge camping is severely nerfed. This cuts down on not just really abusive cases of stalling, but it will also remove the general "regrab it a few times to wait for an opening to get onstage" that we come to expect from Melee and Brawl. Because of this, options after grabbing the edge will probably occur much faster than prior. The only thing 100% faster would be Melee style wavelands onstage immediately, with no multiple edge grabs. **** is mad fast yo.
2. With airdodging nerfed with noticeable landing lag, this stops quite a few camping/running concerns. In Brawl, someone like Wario could literally jump over and through people with airdodges and be totally fine, or airdodge around with platforms. You add some decent lag to that option for landing, and you affect a lot of those scenarios AND punish players lower to the ground trying to get away for free. If a person gets hit or punished from that airdodge lag, they might have been able to get away in Brawl and keep neutral reset or mitigate punishment. Less stalling and more punishment = faster matches
3. The stage list (at least for the DS version) is literally forced to be tiny. Most stages are garbage, and even if you include the FD variations as separate stages, none of them so far really present a super stalling issue. We're probably not going to have a couple of years with stages like Rainbow Cruise, Brinstar, etc. A lot of those larger or more air based stages can be terrible for stalling concerns. We probably won't have much of that for the 3DS, and I mean actual *real* stalling. Not Villager throwing a bunch of trinkets. No, go watch MK players plank the edge for over a minute or go watch me play on Brinstar. Stuff that runs out the clock, not tedious projectile camping. However, looking at some of the characters it just might be possible (hint Wario hint) to still do it for certain MU's.
4. The top 2 characters in Brawl promote camping, while most of the characters below them are varying degrees of camping to begin with. I probably don't even have to explain MK for most of you, but the way IC's promote camping is on the other player not wanting to die from a grab. When some of the campiest characters in the game feel they need to camp at the ultimate level to avoid losing to you, that's a bad sign for faster games lol. MK, Diddy, Snake, Falco, Olimar, Wario, Marth, Pika. Not many of those actually want (or should) approach IC's. The same is true for many of those chars vs MK as well.
4ab. Although it's still speculation, some of the more aggressive characters in Smash 4 look to be more than viable. Sheik and Mac look to be doing a fine job so far. Obviously every region has variety, and some of the campier chars seem to be fine too (Duck Hunt Dog for ex). But even if matches devolve into only projectile camping chars, that will end up being easier to deal with than Brawl's style of camping. If the trade off was slightly longer matches, for actual "gameplay" and player interaction, I'd instantly take that deal. Brawl literally has situations and MU's where you're hardly interacting with the other person: your body stays away from them and you can force wins with it.