I think that the question starts with “will there be an Arduino sketch that implements the lhymicro-gl language?” There’s a python implementation of it in LhystudiosDevice.py in meerk40t to learn from. It feels to me like “1000 lines of code” (more than 100, fewer than 10,000) to implement this language on Arduino, where you would have a much larger buffer to avoid stuttering. You can start reading it from the EgvParser:parse() method followed by parse_egv if you are interested. (Obviously @Tatarize can give a better answer, that’s just what makes sense to be breezing through it.)
After the relatively easy task of parsing the language, I’d think that getting the speed codes right would be the primary challenge for faithfully implementing the lhymicro-gl language on an arduino, since it looks like their interpretation isn’t 100% clearly understood, looking at LaserSpeed.py:get_acceleration_for_speed(). Getting the frequencies and divisors set up to mimic the configuration on the 8051 could well be the trickiest part.
This would probably fit on the attiny84 but I’d be worried about it working with softusb; I’d think you would still want a USB interface chip rather than using softusb. Just like on the m2nano, you might want a schmitt trigger as a gate drive for the mosfet for clean engraving. But attiny84 has two PWM ports that aren’t hardware serial ports, and really has 8 GPIO ports free that aren’t RESET or serial.
But an ESP32 is much more capable and only a few dollars. 
