I didn't want to push the envelope on feature requests but I too agree, DDS would also be awesome to support but if I had to choose I'd still prefer TGA was added into Affinity Photo first.
If its not too much trouble all Affinity team needs to do is implement an exporter for TGA and its the end of the story really. Other than the fighting going on between a few members in this thread (which I hope affinity team does not write this thread off due to that) I hope the points made by several members of why we want TGA support will suffice as good reason to have it added.
If Affinity Team does not want TGA as a core exporter because it does not fit their vision maybe have it as a plugin. This way users could choose to install and anyone who sees TGA as 'bloat' won't see it unless they use the add-on. I'm pretty much looking for any alternative or compromise we can get to have TGA a reality in Affinity Photo.