The Me-163 makes sense of why it was added, each map has a Headquarters for each country and a "Komet" base to help defend it, otherwise without the Me-163 HQ would be down for every country routinely. What is the M-26 going to add to elevate every map? an extra GV that saw almost no action in the war?
There has to be a balance of realism and play ability, the Me-163 brings a strong defense to every map for its HQ, the M-26 would simply be another GV in a long list of GV's to be added.
Sure the Me-163 has 8 kills? 8 minutes of fuel and dozens of dead pilots - it served in the war in squadron strength and flew in combat obviously. However in Aces, it brings a different playstyle when going near HQ.
M-26 would add nothing to play ability.