My idea is to build at least three variants of Pavapro.

1) First is absolutely barebones minimal programmer - two status LEDs (ready, programming OK), single start button and direct connection to target AVR.

Just hook it on and push the button. Simple enough for rewriting arduino bootloader, for example. Though internal EEPROM of Trinket pro is nothing more than 2kB, it shoulld be enough for classic optiboot bootloader or your favourite blink a LED program.

(the box in the middle is trinket pro, sorry for missing legend)

2) Full blown version will contain display too, to show the programming status, so LEDs will be omitted. Keyboard addition will allow to edit the AVR programs "on board" or play snake, who knows by now.

External memory could be I2C EEPROM or SD card, I'm unsure by now. SD card would require SPI bus sharing with target AVR, so the I2C EEPROM looks more reasonable.

Display will be classic Nokia 5110 type or tiny I2C OLED. I'm going to analyse the display and memory possibilities further.

3) This is simply repacked 2) into nice package. But we all know that final look is what matters, that's reason for separate paragraph and even this beautiful visualisation.

My aim is to write software that with a few #define lines user could customize it for his needs (and cover all the options or something in between).