I'd love to see a Venn Diagram of people who support nationalisation and people who support Open Access.
If you mean, is there an intersection of the two sets, then the answer is yes.
As someone who uses the southern end of the ECML, and used to be a commuter, I have a love/hate relationship with open access. The open access operators have linked more cities directly with London, on routes that don't have enough business to support a frequent service. They have been good for places like Hull, Sunderland and Bradford. Politically, it would be difficult to take them away.
But the open access operators take up paths through the 2 track section at Welwyn and platform capacity at Kings Cross. When they started, that didn't matter much, because there was spare capacity. But now there is no spare capacity, the circumstances have changed.
Wearing my economist's hat, the problem is that, if the open access operators can make money running 5 car trains through the 2 track section at Welwyn, then they are not being charged enough for access. Now they should need to run 10 car trains in order to make money. For Grand Central, that might mean splitting/joining Sunderland and Bradford portions at Doncaster, for Hull Trains that might mean doing the same with a Scunthorpe and Grimsby portion.
The difficulty with this is that an operator like Lumo can bid higher than an operator linking places like Hull, Sunderland and Bradford with London. Lumo reminds me of the Highwayman, and in more ways than one.
I don't have a problem with open access operators sharing 1tph off peak in and out of Kings Cross, providing that they serve cities that wouldn't otherwise have through trains, and that they use the capacity properly by running 10 car trains. But I wouldn't allow open access operators to duplicate through services already offered by Great British Railways.
Furthermore I would extend this approach, by giving Great British Railways the opportunity to withdraw from other routes that don't justify a high frequency service. Here I'm thinking of long distance cross country routes using short trains to provide a high frequency service even though the people travelling end to end are a tiny proportion of overall usage. The example I would use here is another location where there is no spare capacity, and that's Ely. The main reason why there is no spare capacity at Ely is that, by historical accident, lots of paths are taken up by short trains running long distances, Norwich-Liverpool and Stansted-Birmingham. I would let Great British Railways out of providing services like these, so that it could concentrate on the big shorter distance flows through Ely, which are Cambridge/Stansted to/from Peterborough and Norwich. If there really is demand for long distance connectivity cross country, then it should be for open access operators to provide it, just like between London and Hull, Sunderland and Bradford.