Atmega8 can be used for boot loading another chip by making USBASP programmer using Atmega8. Can we make USBASP programer using ATTINY85 chip? I guess flash is not a constraint. Any other constaraints?
Had you took a look at the data sheet?
The attiny85 only has 8 Pins. No place for a Crystal for correct USB communication timings. It also has no SPI but a very limited USI interface.
Buying the right controller would be much easier than redevelopping USBASP hard/firmware to use an tiny85