That's a good question. Shockwave was based off ToyCo's Astro Magnum figure, but unlike other non-Takara G1 moulds, Shockwave WAS released in Japan by Takara... so either Takara acquired ToyCo or they managed to acquire the rights for Astro Magnum's mould.

So Takara must have had the mould at some stage. The fact that Takara have never reissued Shockwave before leads me to suspect that either:
+ Takara didn't own the mould but they were able to get ToyCo to manufacture the toy for them
+ Takara had the mould but it has since become lost or destroyed.

...so given that, I'm not gonna believe that there's gonna be any Shockwave reissue unless I see some evidence.