Thanks @Diogee for the detailed statement, I really appreciate that.
I think the current guidelines will fit at least my needs, but I can also imagine that the addressed specification of the rules can be necessary at some point in the future.
@tf2casperr Of course your post also discusses the third-party OAuth limitation, but I think that your idea in particular is also more of an issue with other parts of the guidelines, like e.g. …
Extensions may not transact or encourage the transacting of monetary exchange in relation to any non-Twitch/Amazon commerce instruments.
… depending on Twitch’s valuation of Steam asset/item trades being monetary exchange or not.