Welcome to the forum! 
Yes, we have considered adding in this option! The main concern is compatibility across devices/how users could type it in especially if they can’t configure their keyboard to do so.
The main path forward we thought of was to have a pinyin->zhuyin typing conversion for those that want to learn the zhuyin of characters/words. e.g. z → ㄗ. Thus you still have the pinyin (which is necessary for the mnemonics) but you also get familiar with the zhuyin for the benefits you mentioned.
This makes it so one wouldn’t have to constantly switch keyboards while doing reviews, too. I wouldn’t be sure how directly typing bopomofo would look like with the mixture of meaning/pronunciation questions otherwise 
If you have opinions on how bopomofo support would look like, let me know 