Beside, it's not like Quincy skills and abilities are limited to Quincy. Actually anyone with a good control over their power, should be able to use their skills (strangely enough, Ichigo doesn't belong to that group, since he sucks at controlling his power, which makes the whole situation even more bizarre ;P).
If Ichigo were to master all of the Quincy abilities, then he would be too hax with his own spiritual power several times that of a Captain class Shinigami (sometimes even a few dimensions higher than that) and additional reishi absorption from around. Then again, the current Quincy are able to use Bankais that they have stolen, so I guess the mixing between their classes already happened.
Bach currently is the strongest Quincy and have obtained the strongest fire type bankai, has the strongest quincy spells, his arrows are sharper than Zans/Shikais, has great control over blood skills and probably can enter the Complete Form, what's more it's possible that the stolen bankai might reach an even higher form thanks to the Quincy Complete Form... I guess Ichigo being a Human-Shinigami-Hollow-Fullbringer-Quincy-X hybrid might just barely be enough.