Westworld is technically a movie spinoff to TV. yeah, I'd agree it HAS to be HBO, Starz, or Netflix to be really good and limited to a 10 episode season.
Could totally be a Hitman or modern day Assassins Creeds kind of show, just focused on hitmen going about their jobs and maybe slowly building up a story arc over seasons. The big problem is that at some point people will want John Wick in it, which I guess could have a small tie in around the time of John Wick 3, JW4, etc.
Also might be great as a comedy, sort of like Powerless but done better - random guys who aren't assassins having to deal with the shit assassins leave behind. Probably not work that well since comedy is hard, but in the right hands would be crazy and solve some of the budget problems.