Simply put, make transmutation spellfocus scale haste spell's duration, akin to aura of vitality.
I'd also like if mass haste was included into that as well.
The reasoning is, it seems overpowered at first - after all, well, that'd be an hour long haste spell.
But the thing is, we already have multiple classes that get literally and almost infinite haste from their spellbook/class features, such as:
Warlock (Any greater pact. Very little sacrifice too, just grab extended spell. Only affects single target haste.)
Invoker (Hemomancer and elementalist recover focus. Especially elementalist. They also have mass haste, so possibly a good uptime of party-wide haste. Very little sacrifice.)
Frankly -any- dex build with blinding speed, with varying uptime (Rogue/IB for example has just permanent blinding speed). This also has a notable advantage of being undispellable, but a notable disadvantage of not accelerating action speed, and being removable from your opponent by using a single haste wand charge on them.
Also a honorable mention of a transmutation specialist wizard due to them being able to flux haste. I know, from experience, that when doing party PVE this results in effectively permanent uptime of party-wide haste. It -DOES- come at a downside of being unable to cast any conjuration spell, with some of them being some of the best spells in wizard's arsenal (cloudkill for example, and gate.)
The point is, we already have multiple sources of permanent haste. And it's been proven that it's not overpowered.
And yes, i am aware that haste is one of the best buffs in the game.
But it's also borderline essential, and widely available. Everyone relies on it.
Plus It'd make transmutation spellfocus actually attractive beyond teleporting and losing more stats to a dispel.