maybe you also have to spend souls to teach them the shouts. give, ie, Aela the ability for a day, at the cost of a soul. but you have to teach her the words, using another soul per word, so she can perform the shout at any time, so long as she has the ability.
So if i teach her Fus, Yol and Feim, Aela can use those words when i give her a soul. if the day is over, and i give her another soul next week? she can still use those words. the sound files, animations etc are all there, so it's just a matter of adding a 24hr "Dragonborn" spell effect, which allows them to use known shouts
this. perhaps each perk costs more and more souls as you buy perk points. like DG's werewollf tree.

With a heavy cost associated with it (100 Dragon Souls for example) it would be hard to abuse, but you have a point that I did think of. I was only saying that a respec at-cost wouldn't bring the game to full-stupid where I wouldn't play it.

The only problem with that is that they would have to get all the voice actors back in to get them to have shouts, and hearthfire proved it isnt all that easy to rehire the voice actors

It is only flawed if you are Master of All Trades in which case it is not flawed but intended: you either fully specialize in few skills (aka perk trees) or partially in multiple. Unlike its predecessors, Skyrim supports class-based playing (yeah, it is ironic that class-less game is most class-centered ) rather than give you ability to master everything.

It has to make sense in the context of the game though. It can't just be a skill tree that "Uses dragon souls". The abilities have to make sense. It should focus on strengthening things that aren't at risk of being broken too... Elemental Damage and Critical hits come to mind. Both are nigh-useless in the game as it stands.

Yeah, but in your example, you'd be cheating a stupid crafting system, so it's okay . (aka you should be able to buy a dwarven crossbow.. not have to smith it )

Seriously... you can't pay people to enchant or smith powerful weapons for you? Guh... my mages in DF/MW/OB couldn't SMITH their own armor for Petes sake.. that's why they had tons of gold..

You should be able to make dragon shouts. taking words and combining them. Say unrelenting force+soul tear(from dawnguard. ithink,)+fire breath. u have a new shout called unforgiving life fire. (idk i jus made the name up). but u cant use contradictory shouts like fire breath and ice breath.

Agree, shout combining would be a good idea.
No need to make it convulated and give special names tough: just allow the player to take words from shouts and mix their effects (of course, every effect being weaker than with original shout because less words are used). Optionally allow him to name his own combinations.

probably they'd just use the voice files that the PC uses, since it has voice files for different races and genders, i believe.

but, if we can make shouts with three words from other shouts, say i pick Fus Yol Feim, if i only say Fus, then it would seem silly to send a blast of energy, fire and become invincible, since Fus is the first word of Unrelenting Force

Unless the shouts actually complemented each other. Take as an example the fire and frost breath with the Thunder Shout. The first two would create some humidity so shock would strike stronger on enemies. Or Unrelenting force and Whirlwind sprint. You would charge the first while going at high speed and when you finished the sprint, the added speed would power the push. Maybe a third shout-dragon so we can "fuse" them? Soul tear and Marked for Death also comes to mind...

YESSSSSSSSHHHHHH