1) Slight HP Buff to the Siege Tank in Tank mode
Similar to the Hellion/Hellbat, it would only make sense if the tank is given an hp buff in its less vulnerable state (aka Tank Mode). This would help Terran to defend early aggression from Protoss (Blink Stalkers, Warp Prism Pressure) by making Tanks more durable.
On the other hand, this would hardly affect TvZ at all, since unsieged Tanks never really played a significant role there due to the plethora of counters available.
2) Making Warp Ins via Warp Prism require energy
By limiting the number of warp ins available per Warp Prism (25 energy per warp in would equal 8 units max, 20 would equal 10 etc.) it would become what it was originally intended to be: a tool for harassment rather than for warping in entire armies. Additionally, the time period between each harassment would be drastically increased, since waiting until enough energy has been replenished would become a necessity.
This would allow new methods of counterplay (e.g. EMPs) as well. The Warp Prism strength in PvP and PvZ would be weakend, too, so one has to keep a close eye on that.
3) Thor's Targeting Priority in High Impact Payload Mode
This is more of a QOL change than an actual balance suggestion. Thors have become a useful tool in defending Carriers due to their superior range. When in High Impact Payload Mode they still prioritize to attack Interceptors rather than the Carrier, which makes little to no sense. Considering Carriers require barely any focus during a battle, it would only be fair, if Thors would require a similar level of attention.
Thank you for reading!