Thank you for the information. I am preparing to switch to the new API at some point and just trying to see how much of a pain that is going to be. I'm glad to hear the old API will be supported for a while to come.
As far as the SDK goes there is generally a pretty heavy split there. Some like them while others do not. When working with JavaScript and Quick Base I find using an SDK to be very valuable and it makes everything easier. I don't use one that is made by you guys though, there is a node version someone else released. Switching to a RESTful API will make it easier to work without an SDK so maybe one isn't needed. We currently use a heavily modified version of the c sharp SDK you have posted to Github. Comparing the calls we normally use to what is available in the new API there are several that are currently missing that we would want to see according to other users here I spoke with. I don't have a list in front of me though.
One other thing I noticed is I saw the original page speaking about moving the SDKs to Github.
https://www.quickbase.com/blog/quickbase-sdks-now-on-github It said "I encourage developers to contribute to the repository and make it even richer than it is today." and I would love to see that. If you do decide to have a new SDK it would be awesome if it was more of a community driven thing. If a pull request is put in where the community is trying to improve it it would be great to see them used. I mention this because looking at all the SDKs on there right now many have pull requests from 4+ years ago that are still not merged. The community wants to help but I'm sure there aren't many new pull requests because they can see the old ones are generally ignored.
I guess my main point there is that if it isn't maintained at all then it is kind of pointless to have an SDK. They are good bases to get started even now but many(all possibly?) of them have some huge issues at this point if a new user were to try and use it. It is almost a detriment to have them available because of this instead of any kind of help which is a real shame.