The 800 and 900 DHO's share the same hardware platform, the AWG is just a piggyback plug-in board that has been added to the 900 (plus a handfull of unpopulated components on the '800's main board, mainly connectors, OpAmps and PSU silicon that are populated on the 900 model). The two models also share the same software, configured accordingly. Hence, the bugfixes for the 800 also affect the 900. As yet, Rigol doesn't seem to have addressed/improved their poor Bode plot implementation. If / when they will approach this, noone can tell. Over the time, I came to the conclusion to consider any instrument to stay the way it is at the time of purchase, don't take anything for granted or expect any "could be's". You will almost certainly get disappointed...
Regarding the AWG of the 900 model, I'm not aware of a hardware change, so the coupling in the higher output voltage swing ranges via the power rail is probably still present, but it's not so severe that it would make the AWG unusable for general jobs. When comparing it to a stand-alone AWG, you should rather have the (almost always available) second, identical signal channel in mind as well as the connectivity (reference input, sync/mark output, external modulation input etc.) that are available to more or less extent on the stand-alone models. Moreover, software support may be better (but check that before placing an order, depending on the make/model, you may be up to a surprise...).
If you haven't got any particular use case in mind and just want a "minimum footprint" solution, the 900S may still be a good choice, especially since the integration of the AWG into the user interface is much improved vs. the older models due to the touch screen. Be aware that the probe set for the digital channels comes at a steep additional price or may require considerable effort to make if you favor the DIY solution. Price-wise, I'ld consider the two options on-par.