I thought this was going be a more technical oriented video about what I'd sound like with the performance of the sound chip and the speaker, and the cartridge memory size limitation, bit sad it isn't :(
Fire Emblem supports peaked with FE8\FE9, few are stand outs in FE6 and FE7.
After FE9, supports became even worse than before (FE10 is full of generic "how are you", "let us fight together", "yes we are comrade", FE11 has none, FE12 has very few good ones such as Arran's (very tragic character that was not explored enough), FE13\14\15\16\17 is post 2013 generic anime tropes galore)
I think that adding voice acting to older games, as in the proof of concept, is a bad idea. Players already have mental "images" on how characters are supposed to sound like, so there's a high chance that even good voice acting would rub them off the wrong way.
The picture changes for newer games - like, it would be possible to develop new GBA games to use with an emulator. Then voice acting becomes a matter of cost vs. benefit - good quality voice acting tends to be expensive, but it makes wonders for immersion; while poor quality voice acting would probably make a game worse.
There is one very easy solution: toggle-ready voice acting, so that if one played the games already, they can keep having their canon voices play in their mind as they read the characters dialogues.
Well, voice acting can be very cost-effective if high-quality models are used for tertiary characters, for instance, such as "generic soldier #2" and the likes.
Being able to turn it off makes it even less cost-effective - because as soon as a player turns it off, the cost spent on voice acting is wasted on them.
Your mention of models brought me some idea though - text-to-speech could make this considerably cheaper, thus more viable. And if the voice actors are decent enough, they could be even used for multiple main cast chars, to bring costs down further.