The concern can come from anyone, but that doesn't mean it isn't manufactured. Especially as I mentioned, there has been no precedent for it. If it were something that has been done since the inception of the series, and not in this case, then we're all entitled to be outraged about it. But this ain't it.
Just to break down some of OP's points.
No, this doesn't signify anything and this is just the OP making assumptions. Game Pass only promises first party games on day 1, it never promised additional paid content for them as well. That is entirely up to MS's discretion.
Betting on subscription model as the only way of operating a platform, for now, is flawed.
But none of the three big console manufacturers are doing that, nor have they said that there are any plans to do that in the coming year(s).
Because DLC is made within the existing framework of a game that's already out, and it's generally put out relatively quick after a game releases in most cases.
They could very well have held onto it for the next game, but that would be so many number of years in the future. By then priorities and concepts could and would have shifted so drastically that it may not make sense to revisit that one idea about hotwheels.