So I happen to be zwifting on a kinetic smart trainer using a 2012 Marin Palisades Trail mountain bike with a 22-32-42 chainring and 36-11 cassette
I’m happy to report that a have the issue of getting close to running out of gears due to my improvement… Tough problem to have 
To upgrade bikes to anything with, let’s say, Shimano 105 would easily push over $2K
That being said I’m thinking of just swapping cassettes to an SRAM PG1030, 1050 or 1070 with either 28-11 or 25-11 spacing (about $150 including tools)
This would help out with the wide jumps between gears which I find annoying… for example, downhill with 42-13 too easy but 42 -11 too hard… After upgrading I’d be able to use 42-12
I don’t like to assume anything so I’m asking if anyone sees a problem or issues with my plan. I am mechanically inclined so doing the job is zero issue
Thanks
That seems reasonable but you can do better than $150 for all the parts and tools if the cost is a concern. The main consideration in my mind would be if the 42x11 is a big enough gear. For many people it would not produce enough resistance in a sprint. Also if you lower the Trainer Difficulty setting in Zwift, it will increase the resistance on descents, which you can use to fine tune the experience.
I wonder as well about 44x11 as being too small of a gear but as it sits right now it takes a massive effort to spin up 44x13 down a long hill (like the twin bridges loop approaching the start/finish line) for me to even use 44x11 (44x12 would help a lot I think)
I’m thinking that may become a ‘good’ problem to have down the road but can’t see it happening anytime soon… Although I hope I’m wrong
Being still relatively new at zwift I haven’t looked into the settings but will be sure to do so
Thanks