I think the balancing aspect of giving the Ostheer trenches or other similar abilities to the allies could work, but honestly if anybody is concerned about balance they should raid Relic HQ and demand some answers (like why every German unit in CoH can outperform any Allied unit, each has waaaay better upgrade options [Panzerchecks for everyone? C'mon!], can purchase veterancy for ALL units, has stupidly tough and powerful tanks, AND can use GOD units like Knight's Cross Holders or the King Tiger/Jagdpanther).