> because the invention languishes undeveloped for 20 years. This could be fixed. One approach that comes to mind is to require a sub-20-year renewal process

> because the invention languishes undeveloped for 20 years. This could be fixed. One approach that comes to mind is to require a sub-20-year renewal process that, if not followed, terminates the patent. This might be due to simple non-execution (e.g. patents held by a defunct company, or entities otherwise unable/unwilling to pursue development), failure to pay renewal fees (e.g. you must pay an ongoing lease on your monopoly right), etc.