MEGA328PB support?

Is there support for the newer MEGA328PB yet? The addition of another i2c port is exactly what I need.

Why do you need two I2C ports? Are they pulled up to different levels? You have parts with the same address? Something else?

CrossRoads, yes we have two smart battery packs with the same address. Linear Tech makes an address translator chip but having a second port available seems like a better solution.

All you need is a simple mux to select which one see the clock signal.
Sometimes all you need is an inverter driving an address line at the device - always talk to the Address line = 0 address; control which device has the line Low and which has it High to select who you're talking to.
Or, control in the same manner who see the clock line toggling - no clock, no transfer.

You’d have to figure out where the new pins would go.

The new UART is on the same pins as the old SPI port.
The new I2C port is on NEW PINS, so you could conceivably either route those to the SDA/SCL pins on the R3 (and leave the others on the analog port), or add a new “Grove-style” connector. That would work pretty well.
The new SPI port shows up on ADC0, ADC1 (current analog pins) and a new pin ADC7.

The new PWM outptus show up on new pins (two share the same pins as the new I2C)

So the “easy” change is to make the existing SCL/SDA pins into general purpose (and independent) GPIO pins, with both PWM and HW I2C capability.

328pb have also 5 timers instead 3 !
2 supplementary numerical I/O

Only Arduino management can answer your question.
Unfortunately for you, they can't do it because Arduino is not a non-profit organization.
Arduino has to pay salaries to its employees, and to its founding members.
They have many boards in stock with former 328P. Even if they work to adapt the libraries they do not tell it before they have sold maximum board in stock.

A sign : on Ebay, before the 328pb announcement, micro-pro and nano boards were sold around 5/6 €, since the 328pb announcement they are sold for less than 3 €. You can find Micro-Pro at 1.35 € !
I guess it indicates a massive destocking. Don't forget for obtaining very low prices, manufacturers purchase micro-controller by 100,000 or more rather than 1,000.
What is true for China is also true for both Arduinos.

One word: Patience.