And 2GSps is really something, its should be possible to look at near 1GHz RF, such as 433 or 800MHz china RF module digital ASK modulation, something 1GSps scope is incapable, even if frontend BW is hackable. But then which type of guy are you?
I would not stress potential hacked, extreme-bandwidth applications here. Very few users will try to go there. But even without considering hardware hacks, it is worth mentioning that 2 GSa/s (as in the SDS800X HD) are sufficient to support 200 MHz bandwidth in 4-channel mode, while 1.2 GSa/s (DHO800/900) are not.
Also, if one has any plans to use the logic analyser option in the future, the Siglent scopes will still have 2 GSa/s available for the analog channels, while the DHO900 will cut that sampling rate in half. (But the Siglent has other limitations, due to the fact that digital data are acquired by an external FPGA subsystem.)