According to German sources, HTC may be ready to respond to Apple's move of using the gold/champagne color on their aluminum iPhones. Since HTC uses aluminum, too, for the HTC One, it seems they've decided they should do that, too. From what it looks like, they will be using the same type of paint/coloring process as for the Vivid Blue version. I'm not much of a "gold phone" fan myself, but I could see how some people would be attracted to that, which is probably why HTC is going for this, too.
However, if HTC is going to launch new versions of its HTC One, they might consider launching another flagship altogether. But it would be best if they made a significantly different device, otherwise the people who have just bought the HTC One a few months ago won't like that very much, just like they people buying the HTC One X were very upset about the HTC One X+ a few months later.
Samsung has the Galaxy S flagships for spring, and the Note ones for fall, and HTC could follow the same strategy. I'm not sure if releasing a larger phone would work for them, though, and at this point it would be very hard for them to replicate the S-pen strategy, too, since they need apps that take advantage of it, too.
I think HTC should pursue the photography strategy, and release a phone in fall that is really focused on photography. They've already sort of done that for the past 2 years, but their cameras have also been hit or miss so far, like really good in some areas, but not that great in others. The HTC One camera is great, or probably the best right now, in low-light but because of the low 4MP resolution, it doesn't do very well in good lighting conditions against the competition.
HTC could, for example, release a phone that has a much larger resolution, which gives them the flexibility to either use a higher resolution, and either keep that for the details, or use something like oversampling, or keep the resolution lower (but still higher than the current one) to continue promoting the "ultrapixels", but with much better resolution.
My guess is HTC won't release anything like that this fall, though, and they'll probably just release different color HTC One devices, and perhaps the HTC One Maxx tablet. So far HTC hasn't had a lot of luck with tablets, so it remains to be seen if they can make some money from new devices this fall.