this has been answered several times in past
its working as advertised, network is healthy, developer is alive
improvements to bitcoin are also improvements to viacoin and vice versa
stuff takes time
Exactly this. If Viacoin rebases on top of 0.13 it will get a who bunch of new features like BIPs 9,68,112,113,141,143,144, libsecp etc. I'm not saying it will be easy, or that I will do it for sure. I would certainly like help in reviewing such a rebase because it's quite extensive and risky. There is no immediate need to make such an update though it would be a nice addition making Viacoin compatible with payment channel stuff like LN. In any case, Bitcoin Core 0.13 is unlikely to be released until I would have thought Aug/September so there's nothing to do until then anyway. In the end, I cannot force people to use via. But what is important is that things works. There's no chance anything can be successful if there is no security or stability.
On the other side of things, in hindsight, I'm not convinced 24 second block targets are such a good idea any more, certainly not at large scale. I do think the future is more in payment channels because payments are instant and in terms of usability, that seems like the more expected behaviour. But anyway, not really much we can do about that now.