A better spin blocker definitely sounds great, though whether it would boost stall more than offense... questionable.
Also, an ability that removes hazards on entry (not all at once maybe, but how about 1 layer of Spikes/SR at a time?).
Honestly, the bigger problem with stall doesn't stem from a lack of new/exceptional defensive/utility Pokemon. On the contrary, defensive Pokemon are really popular-- except we're seeing Deoxys-D, Ferrothorn, Skarmory, Tentacruel, Jellicent, Forretress etc. on offensive teams, not defensive ones.
The problem with stall is not access to good Pokemon. Let's face it, some of the very best defensive Pokemon (like Deoxys-D, Xatu, Sableye, and Mew) play a big role in ruining the stall strategy.
The real problem with stall is the increasing number of threats (offensive AND defensive) that decreases the viability of countering every threat in the metagame with a set of 6 Pokemon. Yes, even new defensive Pokemon bring a new threat stall has to deal with, and it still only has 6 members to do it.
No matter how many awesome defensive/utility Pokemon GF chooses to include, you still only get to pick 6 of them to try and counter everything when you go for a stall team. When you build a stall team and ladder, it's not 6 v. 6-- it's 6 v every threat in the metagame; a number that seems to continue to increase as new threats are introduced, and as even UU Pokemon become more and more threatening in OU.
Then we have to add in the fact that GF has to make buck-- the game has to feature Pokemon that will create hype and impress its customers. What type of Pokemon do you think best excite the target audience of elementary school boys? Fucking bad-ass offensive Pokemon, duh-- you need to include a number of Scizors, Garchomps, Metagross's, and Terrakions. GF can't avoid making them if it wants to keep Pokemon profitable.
So, there you go-- I don't think "fixing stall" is something you can do just by adding more Pokemon; especially not in a corporately viable fashion.
tl;dr: Stall's problem is having only 6 Pokemon to counter everything (off AND def threats)-- and "everything" just gets bigger and bigger.