Ulthuan

Now that we have access to the best shooting units in the game as well as the best scouts, do you think an all ranged army is viable?

I would imagine it being something like this:

Lord - Alith Anar

Heroes - Shadowblade, Assassins, and Waystalkers

Core - Glade Guard with Hagbane Tips

Special - Shades and DE Reaper Bolt Throwers

Rare - Waywatchers

Tons of MSU's. Tons of Scouts. Very little to deploy against. Very difficult for an enemy to use any strategy they have prepared for beating any other type of list.

Yes. Assassins really help in this regard. The question is whether it's better than having a single counter-charge element (like WE usually do with their wild riders). It depends on meta.

I guess my thought was that you would screw with their deployment so much that it would make up for not having counter-charge units or anvil units. You would, for the most part, be able to place your units wherever you want. They would have to spread themselves so thin that shooting units would be able to deal with them without the static combat res offered from cavalry or bigger melee units.

While true in principle, there are certain builds you simply -cannot- fuck the deployment for. Examples include Dwarfs with gyrospam, Lizardmen with skinkspam, DoC MSU, Chaos Dwarfs (trust me, they'll take the best corner regardless) and possibly a few more. These are all strong builds. While having a deployment advantage is a big deal, it's not the end-all of the game.

That said, you might do just fine without counter-chargers whatsoever. You'd have to playtest and see I think

While interesting, I personally don't think this is viable. As Curu aluded too there are a fair number of lists that this build will struggle to deal with. In particular armies with a lot of return shooting will do some serious damage to you, specifically I'm thinking of multiple magic missiles i.e. wandering deliberations slann or the loremaster, etc. Anything that can get to combat with you will also make short work of the list.