The problem is, say they reach Gen 10, that's at least 1,000 Pokemon if they keep to adding roughly 100 each time. Catching 'em all in those games will be a nightmare. I'd love for them to keep making new games, but there's going to be a point where there's so many Pokemon that people will forget about the majority of them and not really care about them. I mean, we're at 493 in the actual games right now, and I'd say 200-250 of them I couldn't care less about. Come 1,000, that's around 500 at least.
I reckon they'll reach Gen 10 easily, but after that I'm not so sure. I just hope that the Gen 5 games are really different compared to the past 4. The formula is starting to wear thin for me. Don't get me wrong, I love Diamond, but I feel there's so much more they could do with the franchise other than just doing a copy&paste job with new Pokemon.