The F-16 seems to keep receiving updates and new aircraft appear to still be in production, e.g. the F-16I and F-16Q. It seems there are also several upgrades being developed and installed, such as radar (AESA) and radar detection warning systems.
Has any authority on the subject attempted to estimate how long the F-16 is expected to be in production? Is there any estimated limit on for how long a budget fourth generation airframe can be used as the basis of a modern combat aircraft?
I'm not looking for speculation from StackExchange users but rather a reference to a statement made by one or several external authority -- to avoid making this question opinion based. Some sensible original reasoning is only a bonus as far as I'm concerned.
I can only imagine myself that countries that keep buying F-16s do so for budget reasons -- however, there must also be some real value in buying F-16s in 2019, since these are after all large sums of money even if it is bleak in comparison to e.g. F-35s or F-22s.