It's possible to do double boot by yourself. But it's very risky, 'cos U need to change EE's boot loader to custom one and there probably may be incompability with update mechanism used by EE.
On the other hand, I don't think that EE tech will make double booting (or even allow to use custom firmware\os) due to marketing plan. It's the same reason why many hardware manufactors officially support only one OS (making you to buy new hardware in order to keep modern OS), or restrict the use of VoIP (making you to use expensive mobile calls instead of cheap skype), or limit the compability (in order to buy e-book only from their own store). e.t.c. It's stupid marketing, but it's reallity. The only way to get what you want -- to do it by yourself, or with the help of people who also has an interest in it.

Previously I asked if there's some people who interested in custom developing for EE, but didn't get much response. Also as far as I see there's no many people with needed level of expirience to make custom firmware for EE. And I, by myself, also don't so good to make custom firmware alone, and not so reach to pay several thousand dollars to hire people who can help write what I'd like to get for EE.