I now believe Erik and Andy will not let AVR sweep the 8051 :)))
It is not up to us

My opposition to using an AVR
1) It is an Atmel, that is persomal, so disregard that for your purposes.
2) Single manufacturer. If Atmel backorder you for a 500 day wait, you are screwed. If a '51 manufacturer tell you the same, you go to another. Even, when using very specific derivatives, the chyanges in that situation are nominal.
3) Non-optimal tools. The IAR compiler is a 'universal' compiler with a chip specific 'front end'. Such a compiler can never be optimum.
4) Limited range. In the '51 world you can go from a LPC900 to a 8051F120, the 'bottom' for AVR is higher and the 'top' is lower.
5) It is Atmel, tell them about a defect and they will reply that it does not exist.
6) if you live (Ap still will not enter location in his profile) in a place where Atmel is well represented, you can use Atmel '51s so, if 2) shouild happen you can still (possibly with some trouble) get another brand of '51

Erik

PS the statements above can be applied to the PIGs as well.