After slumbering for a while, Zilog seem to have hit the ground running here, have some nice small packages :

Z51F0410HCX 4KB Flash, 256 bytes RAM, 10 pin SSOP, Lead free
Z51F0811RFX 8KB Flash, 512 bytes RAM, 16-pin TSSOP, Lead free

and 1.8V–5.5V / 12b ADC / EEPROM / i2c in 10pins, OCD all
makes up for the rather ordinary core speed.

looks like they have an on-chip regulator, which should make the Vcc tolerance excellent.
(also somewhat explains the core speed)

Interesting ALU, they quaintly call a 'calculator' on the larger models.

PLL works from 32KHz, good, but perhaps it should be called PSLLL instead, for 'Phase Somewhat Loosely Locked Loop' with a 2% frequency spec ?!

Minuses ?
* Missing from the family, seems to be 64KF in 44 pins, which is an important 8051 'sweet spot' ?
* Also no ALE (or PSEN) pins, which will reduce the application area.
* Timers and UARTS are Zilog unique, which will make porting SW a challenge...

Be interesting to compare these with Holtek, when more info is released.