IMHO the H90 is a ridiculously good value for anyone deep enough into the H9 to have two of them. If you plan to sell two H9’s and you live in the US, an H90 might cost you $300, net.
It adds 10 algos right away and this is the beginning of a product lifecycle that might last 10 years. Additional algos (free or otherwise) will come and they make the value proposition even more compelling.
Since the H90 can operate on two separate signal paths, I bet you can swap out 2 of your H9’s will little modification.
I have imported about 200 H9 presets (three lists). That went smoothly except that I had to manually assign an expression pedal to the ribbon controller ranges of my H9 presets. Meh. Not that bad. In practice, I’m only using about 12 preset pairs on a regular basis anyway.
There’s a lot more, but IMHO that much is already a no-brainer.