Regarding Red vs. Blue balance, the fact that DCS takes place in Russia/Georgia means that situations are hypothetical anyway. The 51st server has awesome mission design, and keeping a strict plane selection based on East vs. West is great, as it is closer to reality.
Saying that, having both East and West jets available to both Red and Blue does not bother a lot of people and gives different options. Personally, I enjoy the realism of flight/combat simulation the most. Hypothetical scenarios don't bother me and have certain advantages.
When someday we get more theaters to fly in, we''ll be able to recreate historical senarios much more, but having the same jets on both sides, and jets from different eras will make things interesting as well. I am looking forward to flying the P-51 as an option for ground pounding.