My guess is that if the democrats were to put forward any kind of legislation to expand the court it would along the lines of what
@Sinn Feinhas been promoting except it would do something like add a tenth justice in 2025 and an eleventh in 2029 and twelfth in 2033 and thirteenth in 2037 and split a circuit for a fourteenth in 2041 and get back to odd numbers splitting another in 2045. They would then beg for bipartisan support and add a bunch of very GOP friendly provisions elsewhere and then when it came up for a vote their would be no such GOP support. (Even though this entire idea means there is Supreme Court justice on the line for next 6 elections which I think benefits the GOP more than democrats - at least in the beginning.)
But I would need big odds to even contemplate such a watered down version. Maybe this time is different and the recent Trump and GOP activities were the last straw,
but democrats just don't fall in line like republicans to pull something like this off and thus their leadership doesn't try. If they did Trump would have been impeached at least two additional times by now. (When the Mueller report came out and practically begged for the House to continue and for emoluments.)