I'm also concerned by some of your changes, e.g. to the XML parser and the string hashing algorithms.
I don't think anyone plans on running 7.4 _code_ in a few years time, but they may very well have _data_ that conform to rules introduced back when 7.4 was current. For instance, some of Roxen's customers have websites with hundreds of thousands of XML files in repositories where they could have markup errors that these relaxed parse rules were introduced to cope with, or there could be custom modules or databases where the 7.4 string hashing is used for checksums.
I'd appreciate if changes with potentially high impact are discussed here before being committed.