I think by the time the third or fourth season rolls up it might be time for another 'big' episode. By this time kovu will have made at least one episode, and I don't think they'll show kion as a cub forever.
As other people have mentioned, the show will need something to explain why kion was missing from the second half of tlk2 assuming they ever go to that point. They might not.
I'd say that the season 2/3 season finale should be kion and his guard going on a mission outside of the pridelands. It's a secret mission, so secret that we don't know what it is. Only Kiara and the guard know what it is. It is never explicitely mentioned.
The second tv movie should start a few years after the s2 ending. It shows kovu and kiara happily married with two cubs of their own. One as the future ruler of the pridelands and another as the next leader of the guard.
Kion and his guard return as adults, and there's a big joyous reunion. The thing should be a big setup for the next few seasons where there's a new lion guard, led by kiaras second born. Kion would be like a mentor towards the cub.
This might be a bit too risky and would piss off a lot of fans but simba and nala wouldn't survive this tv movie. Simba would get into a fight with janja and his clan but not survive it. I would also give nala the story arc she has deserved but never got since tlk1. It would be about her dealing with simbas death and her own eventual death.
The ending wouldn't be completely depressing, but I haven't thought of a good ending yet.