Thank you, I didn't know about the route bars being a thing. However, I don't think any of MK/Richmond/Wimbledon are on the line from Paddington to Reading?
This seems like it would cause an argument at Paddington, but I don't see anything in the restrictions explicitly forbidding my proposed route.
The electronic data restrictions apply only to journey planners, so they only limit the journeys that you can get an itinerary. In my view, the Routeing Guide is still a contractual method you can use to determine valid routes - it gives no reference to these electronic restrictions, so they are not a limitation on the contractually permitted routes.
The lack of a Maltese Cross symbol similarly means that journey planners aren't allowed to offer Tube transfers as part of the journey, so you'd only be able to get itineraries overnight when the industry data feeds say that the Tube "doesn't run". However, there is a specific section of the Routeing Guide which makes clear that such tickets are still valid on the Tube when LONDON is a mapped route:
In some instances (particularly long distance cross country journeys) the fares data will show an "any permitted" fare but without the via London, Maltese cross symbol. Reference to Section C (the “yellow pages”) may show via London to be a permitted route for this journey and in such instances travel via London to include cross-London transfer would be permitted.
So I agree that contractually speaking, it is a valid route. But you would probably encounter arguments not only at Paddington but quite possibly at Marylebone too, and certainly I think you would be very lucky to be let through the Tube barriers, if they actually look at your ticket that is.
Almost no gateline staff - NR or LU - seem to have any proper understanding of NR ticket routeing/validity rules, in my experience. I don't blame them for not knowing in the first place as it's probably not covered in detail in their training, but I do find that those who challenge 'unusual' tickets often have a bad attitude along the lines of "this can't be valid so I'm not interested in hearing why you think otherwise".