Shimano XTR has the 10-51 12 speed cassette coming soon. With regard to Eagle, it's awesome - on my mountain bike (wife also loves hers on her Tallboy - she fancy). The X01 cassette weighs 353g on my scale. I first started with 1x10 Shimano gearing back in the day then incorporated Leonardi GL cassette expander (largest 3 cogs on an XT cassette up to 42t), then Wolftooth, etc. They worked well but the SRAM XX1/X01 10-42 11 speed was far superior; the wife now has those gears on her rigid Niner gravel/mtb bike. Eagle is a bit heavier but the 50t solves all sorts of issues especially in the big Colorado/Wyoming mountains. We Okie flatlanders need low gears, big time when doing real mountainous adventuring.

On a road tandem the larger Eagle jumps would likely get on my nerves. On an MTB/gravel tandem, no problem. I even confirmed gravel use with a SRAM X01 10-42 cassette/Force/Red 1X drivetrain on my single gravel bike. It is great and the jumps aren't noticeable. We currently run an 11 speed Shimano Ultegra 52/39 x 11-32 and even then the jumps sometime feel a little large. I may slap the 11-28 cassette on to compare.

Also, SRAM Eagle (and 11 speed equivalent) derailleurs aren't compatible with their road shifters. However a Rival/Force long cage can handle the 10-42 cassette. My medium Force even handles the 10-42 (Red shifters). Perhaps a solution has been released and I missed it? Good conversation!