Not sure how well versed you are on GoPros but how can something that currently supports a Hero 5 which was released on September 2016 be outdated in 12 months??? The 5/6 and 7 All can use the same case.
Also, the soon to be released Hajimoto Collaboration model will support the Hero 3 and 4 which the 3 was released in late 2012.
Hajimoto, having worked extensively for the leading electronics deal for America I've very well versed. If you have even basic knowledge in electronics you would know that the majority of eletroncis in today's world outdate within a 12 month cycle. Same reason people aren't driving around model T's on the road compared to today's cars... I'm not saying older version won't/wouldn't work nor also that they wouldn't produce adequate quality video. The Hero 5 is limited in its video capabilities and will not be upgradable hardware or software wise in the future and that is a fact, period. If GoPro thought their Hero 5 was still current, then they'd be selling them and not a newer version. The versions you'd be making an option for Hero 3/4 are even older and more restricted in their capabilities than a 5/6/7.