Nintendo can't do anything with them because Microsoft now owns those IPs and publishing rights to the older games as well. However if Nintendo bought Rare, I think k they would have exploited those IPs more effectively than Microsoft has. Nintendo has a well desert reputation on exploiting their IPs on their systems.
Except Nintendo culture is vastly different than Microsoft's culture. If Nintendo bought Rare, they would have applied the same Nintendo standards that they apply to their AAA titles. Meaning they wouldn't have allowed crap like Grabbed by the Ghoulies, Perfect Dark Zero, and Kameo be released until they met Nintendo's standard of quality.
They were Nintendo exclusive games because Nintendo owned 49% of Rare, but Rare was still an independent company. Nintendo would often act as simply the publisher of the title for games like Killer Instinct, Banjo-Kazooie, and Perfect Dark, but they were games that Rare decided to make on their own, and as a result, they owned the IPs (hence why Microsoft now owns them). For some of these games such as Conker, all Nintendo did was merely take up the role of distributor while making Rare the official publisher. And they helped with the marketing. Nintendo didn't commission these games.
If Judgment hadn't happened at all we would have had a good gap before any X1 release. I think people would have been excited for next gen Gears with Gears 3 being the last game and maybe 6 months or so after Halo 5. And then a sequel 2 years after that. I think a gap will help the franchise now like you say but the gap itself could have replaced Judgment and we'd have had a 100% success rate on last gen with enough time for anticipation to build for the next gen version. Plus the last game being active rignt up to the next gen release rather than almost completely abandoned. (at least Gears 3 is still active)
Given that xbone and ps4 have AMD GPUs and very nearly the same CPU I doubt there would have been a significant development cost increase in going multi platform.
