This is just a list of things that could be improved in the code. Feel free to add something if you find anything.

GUI

Menu shortcut system (Configuration.cpp contains duplicate descriptions for actions made with makeShortcutAction)
Convert everything to MenuBuilder

DBG

Clean up debugger.cpp and debugger.h. This file currently serves multiple purposes.
Move the database and dbghelp to a separate component.

YzDbg

Supports ODBGScript
Supports memory breakpoints
Supports memory watching similar to CheatEngine
Includes instruction emulator
Shows modified memory of current dump (possible with shadow buffer)
Supports mode of operation that doesn't attach but uses process manipulation APIs
info box shows mnemonic brief in cn.
disassembly preview support dump
can drag the registers view to scroll
support "dd" command which dumps the data and set dump mode to dword.