In the (unlikely) event that $P=NP$ with a constructive proof of a polynomial time algorithm that solves 3SAT, obviously things will be very different. However, practically, it could happen that the degree of the polynomial run time is very large (e.g. $O(n^{10000})$$\Omega(n^{10000})$) such that any reasonably large problem is still out of reach for our current computing technology.
My question is: is it possible to find/construct a problem that have a lower-bound polynomial complexity $O(n^p)$$\Omega(n^p)$ to compute but an upper bound $O(n^q)$ to verify, with $q$ being quite small (e.g. $q=1$) and $p\gg q$. This problem would function essentially the same as current problems for which no known polynomial algorithms exist (e.g. factorization), and thus would still be usable in e.g. security systems in even in the case of $P=NP$.