Some of the features I like from my own splitter are:
* work tables to catch the wood so you don't have to lift it multiple times.
* 3-point mounted so it raises and lowers, allows me to lower and roll on a big one using an old car ramp as a helper, then raise up to the perfect height so I am not bending. that height may change during the course of the day, and certainly changes depending on who is splitting. Even if it has its own engine, this idea may be considered.
*consider making the splitter rotate to vertical too
Here's a thread talking over much of these ideas, and pics of mine are in there:
http://www.tractorbynet.com/forums/attachments/146167-powerhorse-3-pt-log-splitter.html
Honestly if I was starting over I'd reconsider hydraulics altogether. These new mechanical ones are more economical to run and are faster too...
DR Power Equipment - RapidFire Splitter Gallery
DR is one supplier, there are others but I forgot them.