IDA 5.0 free lacks most features introduced in the IDA SDK over the last decade, starting with the extlang support which was introduced in 5.3 or thereabouts and important changes in scripting infrastructure introduced in v5.6 like support for objects, function values, references and properties (a.k.a. 'attributes'). Somewhere along the way there were breaking changes like the passing of string values as VT_STR2 (i.e. the awkward qstring thingy) instead of VT_STR.

This means that current versions of IDAPython cannot be backported without major rewrites and feature reduction. 

Porting the old IDAPython 1.0.0 might be as simple as rebuilding against an implib for IDA 5.0 free but updating it from Python 2.5 to a more recent incarnation (2.7.8 or 2.7.9) could require some changes. The chances are still reasonably good for adapting IDAPython 1.1.92 or even something newer but it is bound to require a fair amount of work.