If I hadn't know, I wouldn't have known Nexus was part of the Future Saga. ACiT for an ending, perfect. In my honest opinion, the series could've ended right then and there. Storywise anyway, cause I neeeeed more R&C. What was I talking about, oh yes. Nexus is… A nice tidbit. But a true epilogue of Future Saga ends with finding the Lombaxes. Not, again, not-finding them.
Nexus is a fantastic game. But it's no more an epilogue than ACiT's ending.
Ratchet found the Lombaxes. or more appropriately he found where they are. But, I suppose you mean, he should bring them back. There upsides, but there are many more downsides. The major upside is that Ratchet would bring back his kind and he wouldn't be alone anymore (although he already has Clank and Talwyn and … Qwark). The downside of their return would be that Ratchet would not be anymore unique, one of a kind. Besides, he knew the risks of bringing them were great and doing so would have proven him as selfish something he has proven he's not since the ending of ToD up to ACiT. Also, Vendra tried the same only to be betrayed by her own kind and to learn that just her closest company-brother, Neftin, was all that she actually needed in her life. And, Ratchet was ready to abandon everything including Clank to "find" the Lombaxes. Would that be a proper ending just to find them? Would it worth it? There is a saying in Greece "Those who seek the most lose even the least".