Would this variant run the risk of increasing the first-player advantage? The 2nd player has even fewer opportunities to gain a tempo on their opponent.
Regarding provinces vs. alt VPs, yeah that's interesting because with provinces the time taken to crank up to 8 Gold per turn will still be the same, it's just the greening phase will be shorter (probably oversimplifying it there though). So maybe with alt VPs like those mentioned you might stand a better chance of winning that race. However it should be noted that half as provinces is half as many points, but - to take an example - half as many dukes (assuming half as many duchies also) is a quarter as many points. This could maybe be the death knell right there.
The gardens scenario pointed out only has 22 cards, so the gardens are costing 4 and are only worth two, and it only gives you a total of 15 points, the same as 2 provinces (including starting estates obviously), where as traditionally you're looking at say all 8 gardens and probably under 50 cards (you bought out the estates say) giving you 43 points, which requires 7 provinces to equal. The Blitz version is much weaker in that sense, so it really does need to be super quick.