Do not expect support for the old versions. I also would not expect support for extensions objects. I have not seen anything in this regard on Idea page of community nor heard of anything like this in regards to roadmap.
I would stick to objects which are a core of Qlik Sense and would work of them. Extensions can change/ will change and support of them is practically not possible.
cheers Lech, When applicable please mark the correct/appropriate replies as "solution" (you can mark up to 3 "solutions". Please LIKE threads if the provided solution is helpful to the problem.