XviD does support QPEL even though it is not turned on by default. You have to manually turn it on (if you feel it helps with your material). Also XviD encoder dialog settings are not accessible via AutoGK (there is a way, but complicated) because then it becomes no different from GordianKnot and defeats the purpose of being an automated tool. Atm, the drawbacks of QPEL are more processor power to decode QPEL-encoded content (minor issue) and limited standalone support (major issue). AutoGK strives a lot towards standalone support by having ESS & MTK/Sigma profiles, disabling packed bitstream, using VBV (if instructed), using standalone compatible matrices (when instructed) etc. If AutoGK enables QPEL, then it will break standalone compatibility for about 90% of the standalones. When there is a wider hardware support for QPEL, len0x might implement it.