One way around Lumo capacity problems, at busy times, would be if 803’s can be coupled up, and there’s spare units, and crews to do it, then run 2 units together, giving a 10 coach service, wether this is in reality feasible, is another thing.
Having short 5 coach trains running services, always gives the same perennial problem, of overcrowding at busy times etc, the railways should have learned this, from right back when operation Princess happened with 4 and 5 coach voyagers, taking over from long intercity trains, and as long a 5 coach trains, are ordered for long distant services, then it will carry on happening.