How about adding the possibility to store the graphs on a different server (by ftp)? I suppose a large part of RouterOS machines is running from flash boot media, so storing the graphs to disk regularly (even only once a day) would put unnecessary wear to the flash drivers. On the other hand being able to keep graphs over the next reboot or failure surely is something even those users (including me) will want.
Of course those could still refer to using an external solution like RDDtool or MRTG, but why not just improve the (new) internal functionality here?