To a lot of people, ARM7 class MCUs are the natural replacement for the
existing  8051 MCUs. There are good and faster 8051s out there but they
often cost similar or more than the ARM7 counterparts.

However I was trying to select an ARM7 MCU and found out some problems
(comparing to higher-end 8051s and PIC18F)

1) Power consumption: in general higher
2) I/O driving capability: in general weaker
3) Some ARN7 MCUs like TI TMS470 do not have 5V tolerant I/O. They also
need dual supply (3.3V and 1.8V).
4) Packaging: lack of small package MCUs in general

In the end we still decided to use an ARM7 because of the processing power
needed and the general consensus to move to ARM7. 8051s and PICs will still
be used when processing power is not that critical.
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