@Fido,
The founders was long term thinkers even those some of them would be surprised that the framework they set up had survive for over two hundreds years.
Now the problem with changing the form is to find a form that is likely to give better results and do the change over smoothly and peacefully enough not to end up destroying the very society you wish to aid.
I think that most people can see we are going toward the rule of a small oligarchy that is harmful to the majority of the people however counter pressures within the current framework might let us go on with our current system for a time at least.
Sadly I see no path forward that will get us long term out of the mess we have been drifting into since WW2 with or without our current government form.
Side note Franklin seem to had agree with you that nothing is permanent as he set up a trust in his will to aid the education of tradesmen/craftsmen in Philadelphia but did not have it open ended but set a two hundreds years time limit afterward the trust was broken apart and the funds donated to a numbers of group who names at the moment does not come to mind.