[AshleysBrain]

I'm all for improving what we have, and the new GSS system does look interesting and could possibly influence CSS. But I think you're reacting too strongly to CSS. AFAIK the normal, flex, and grid layout modes are compatible (in the sense that you can mix them in one page and have things like flex inside grid elements and vice versa). Being a lurker on some standardisation email lists some of the best engineers in the world are on there taking everything very seriously, including future-proofing since everyone is well aware anything they add now will basically have to be supported forever.

I'm not sure I understand your two complaints (isn't there already position: relative and percentage sizes?), but I think good engineering is always about making tradeoffs, and while I don't understand GSS enough to criticise it I feel it's unlikely to be a silver bullet that magically fixes everything in itself, and will likely have its own quirks and pitfalls as well.