This seems to have morphed into another one of those "Complete the Ringways" threads, so …
"Is it time to remove Westway?" - no, leave it alone! Despite the knocking, it works.
I lived in Hounslow in 1969-1971, when the Ringway plans were big news and still a serious possibility. My enthusiastic young self was hugely disappointed when the majority of it didn't happen, but of course it was over-ambitious and over-scaled (esp the Motorway Box).
However, I totally support decent new roads in the capital. Yes, London is a rather special case, particularly the dense historic core, but farther out it should have good road access like any other city. Much as some would wish and believe, private cars are not going away (though, with a bit of luck, most of their pollution will do so). Also, light commercial traffic can't be mode-shifted to rail, active travel, etc; and taxis and buses will always need roads. Sorry about that.
My additions wouldn't include a pointless upgrade to get more traffic more quickly to dead-end Marylebone Road. They would focus on rectifications and extensions to continuous routes, especially the North Circular. Amongst other things, I would -
1. Grade separate Bounds Green. It should have been done properly at the last improvement. I accept that it might be so hard now as to be poor value-for-money.
2. Continue A406 clockwise under the river, to join up with A2/A20 and what there is of A205. This is a glaring omission and would be really useful, despite the plan downstream for LTC. I am aware of stuff (including the wood
!) in the way, but come on ...
3. Duplicate Gunnersbury Avenue south of Hanger Lane and GSJ the Gyratory. This has been described as pointless since it crashes into Chiswick Roundabout, but my plan would be to avoid the roundabout, unless you want the M4, by tunnelling under the river. This A406 anti-clockwise extension would surface somewhere(s) in Kew/Richmond, having split underground (a) towards the A316 radial (feeding the M3) or (b) to join what there is of A205. Somewhat similar to the original R2 plan, but on a smaller scale with longer tunnels.
Some brave engineering would be required for such completions, but technology (bridges and especially tunnelling) has come a long way since 1970.