I've built the new board and tested some features. Have to visit local hackerspace to do more tests.

Conclusions:

• DC works
• attenuator works
• attenuator values are really impractical (not very standard) and I'll probably have to buy them online

To do:

• test AC (need AC source)
• test DC offset (need 10k or similar pot)
• test overvoltage protection (need 9V source for arduino)

I've compiled the scope in windows 7 virtual machine as well and that went without any problems, so after I test the board I'll probably add windows executable to github.