There is artistic value in projects like TF2 Gold Rush - not necessarily as something you'd expect to _regularly play_, but as something you could admire as a piece of art.

We can still use some of them, namely Hammer++.

But if we wouldn't have to keep the result _compatible_ with stock compilers, the world would be our oyster.

We wouldn't have to spend time doing hacks like converting brushes into props to fit meet archaic limits

Propmerging could be automated etc

Most likely, as it wouldn't be shoved into the Misc category that takes 5 screens to scroll down and is not selected for queueing by default.
Also, the community servers would likely have extra VSH-VScript maps in addition to the officially added, giving the gamemode more variety.

MvM Motherland is OUT! #TeamFortress2 #MannVsMachine

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and maybe an SFM short.

If a Hightower reskin was eligible for a Major Update, they could totally do that for the modern updates.

Heck, they don't even need to make the promos themselves - the community would happily do that for them, here's what they did for the VSH Update: summer2023.tf2maps.net