Why can't superweapons not just be limited to 1/galaxy?
Or make them use up a Capital Command slot.
Any of these would require the supwerweapons to get buffed. But at the same time you could have fewer. I would rather have a powerful superweapon, than having the possibility of a TEC player having several Novaliths...
Thing is, Novalith stacking is good for something. Advent or Vasari Supweaponstacking won't win you anything. There's hardly any need for more than a maximum of 2 of those. While a TEC "could" still turtle and just shoot the hell out of his enemies ( as the only viable counterstrategy is building starbases with aux, but thats actually more expensive than a nova... ) ( yeah theres planetary shield, but only TEC got those...).
Or just make Novas unable to finish a planet, make them always leave 1 hp left .