21st century skills are being added onto K-12 educational curricula globally, often via integrating them into existing subjects such as math. Simultaneously music teaching in K-12 education is losing relevance and popularity. Yet, music theory contains logical structures which are in many regards similar to program code. Additionally the digitization of music production requires composers to effectively use digital music production tools and associated technology. We investigate the opportunities technology-assisted music composing offers for teaching 21st skills and programming in K-12 education through expert interviews with professional music composers (n=4) and programmers (n=5). Analysis of the similarities and differences in the thought processes between creating software and composing music revealed the latter to have potential for teaching the following thinking skills present in K-12 educational curricula: modularity, loops and conditionals, data structures, input/output and software design. Additionally implicit learning benefits on increasing technical know-how, cooperative skills and design thinking were discovered.