The thing about Delorme maps is that they are very USA centric. I am sure that if PGC (who are based in Sweden) were to implement a solution for a particular request they would want something that can be applied globally. In this case that would probably mean all the mapping systems around the world - Delorme, NZTopo50, Ordinance Survey maps of Britain - the list is probably huge. Here in New Zealand we have an older system as well, so... one to three mapping systems per country? and each one is unique. As you can see, the problem is complex. And then there is the counties that may still have inch-to-mile maps, before they went metric...
I think the solution for most people will be to do as you do - export the caches and somehow overlay them onto their preferred mapping system, rather than for PGC to cater for them all.