Hello, and welcome to the conversation! I really appreciate you getting down to brass tacks and asking questions about implementation.
Once upon a time we were working on an alternate HDK written in AssemblyScript, to make JS/TypeScript folks feel more comfortable. But at the time it wasn’t mature — there was no JSON serialiser/deserialiser, you couldn’t do closures (pretty much the backbone of JS), and there were only a few data types. It’s matured a fair bit since then, but it’s still not JS proper, so we’re questioning what an AssemblyScript HDK’s purpose would be.
From what I’ve seen, it seems that the underlying raw API is pretty stable — changes are mostly additive these days. So you’d be looking at mostly feature additions with the rare breaking change if you wanted to create another HDK.