They should add Tarhiel into the Morrowind area, at least as an easter egg. Elves can live for hundreds of years, and TESO takes place before he dies, so why not? It'd be sweet to see him in a Mage's guild type thing, and see him getting chirped by his colleagues for having stupid, implausible ideas, which drove him to try to come up with his jumping spell, to try to prove them wrong.

I plan on meeting a younger Fyr, so I don't see why there won't be others

TESO takes place long before Tarhiel probably lived.

Let's count, shall we?

TESO: 2E583
Morrowind: 3E427

About 800 years have passed between the two. Elves live a longer life then humans, but they generally seem to cap out at around 500 years (as Skyrim indicates that 250 is about middle-aged.)
Barenziah was visibly old when we see her in Morrowind, and she was young when she had met Tiber Septum (who iniated the 3rd era.)

Divyath Fyr and the other Telvanni councilers have excessively long lifespans. It's noted in-game that it's because they are old, old wizards who probably have found ways to extend their lifespan. An elf living for 4,000 years is NOT normal, nor expected.

In part IV of the real Barenziah it says elves have lifespans of around one thousand years. And then I remember something else saying that elves who use magic can live a bit longer than that, so I'd say that with 800 years between the two games, it wouldn't be remotely unreasonable to put him in.