Do you have an actual, specific proposal? I've yet to see anything concrete, not even in answer to specific questions I raised. This is the sort of thing that typically gets removed by moderators.

This feature, does it have a specification beyond "implement multivariate series"? What might that spec be? For example what would be a sample input and output? What would be the restrictions on inputs? Holomorphic functions in some region? Something else? Would the result use order terms?

What I'm getting at is I don't see this as in any way a part of the current Series function. A TaylorPolynomial function might be useful. But it would be a different function. I see no way this could be construed as feature missing from Series.

Will such a function show up in a future release? I'm not sure. There is an ongoing project to extend multivariate capabilities in some areas related to this, so it would not surprise me. But I do not have definite knowledge one way or the other.

(1) Multivariate series mean different things to different people. The iterated form supported makes perfect sense and works in a way that requires no departure from univariate.

(2) If what is wanted is a total degree series, the method to do this is fairly well known. It requires introduction of a new variable. I have to wonder how that would fit into the framework of Series? (Short answer: Quite poorly.)

(3) This would appear to be a case of hijacking a thread. It has naught to do with the Series changes that went into 11.1.