Thanks for the replies. To counter the weight issues im moving the handle back a bit away fromt eh center of the case so its almost above where the body of the guitar will be. This is so that any central balancing issues are countered and it'll be easier to carry. Somethign that I personally find annoying is have the guitar tip to one side in the case becuase it's not firmly in position. So far the only way I can think of overcoming this problem is to ensure that the case is compact enough to stop the guitar having too much room to tip to one side.

As for overcoming the problem of different guitar profiles in the case to make it more universal. I've designed a method to have a basic slot for the guitar (with neck support.) and then additional foam blocks can be fixed in to match the profile of say, a Fender Telecaster. These blocks could then be moved and replaced with other foam blocks to fit the profile of something like an Ibanez. This is just an early design idea though. From the looks of it I may have to bring it all down to manufacturing a case for a series such as Fender Stratocaster's or Les Paul guitars.