The ATTINY15's was ideal for designing FCC Part 15 exempt battery powered products since its 1.6Mhz internal RC clock ran just below the 1.705Mhz cut-off.
The ATTINY2/4/85 replacement parts come with a 1.6Mhz compatibility mode, but this clock is derived by dividing an internal 6.4Mhz clock. Since the FCC exemption requires that the device "not generate or use frequencies above 1.705 MHz", this replacement part does not appear to be eligible for the exemption.
It does seem possible to qualify for the exemption by using the ATTINY2/4/85's internal 128KHz clock, but this is much, much slower and not practical for some applications.
With the ATTINY15 dead, are there any good ways to design Part 15 exempt battery powered products that need more horsepower than 128KHz, without needing to resort to adding an external oscillator?