"...If one uses MOVX @R0/R1 then P2_pin=P2 latch...."

This the normal state of P2 and other ports anyway. So P2 can be used as a normal port through the program if the movx using dptr instruction is not used. In fact the Intel 8155 was a wonderful device for such use till the i2c peripherals came along. In fact you may find an i2c ram even a better choice than parallel ram, unless you need real high speed, then RD2 series might be better because the board will be simpler.