A huge design issue that might - or might not - be pushed would be the power system. Solar panels require that JWST stays in the sun while conducting observati

A huge design issue that might - or might not - be pushed would be the power system. Solar panels require that JWST stays in the sun while conducting observations, while at the same time being critically dependant on the observing equipment to be cool - and being unable to just keep it inside bigger structure like with Hubble. This means that there's a huge problematic sun shade structure which is considerable part of the SPOFs still endangering JWST even if it is inserted into orbit correctly.