For reference just in terms of pure energy a 150kg weight to overestimate the weight of things such as a Ranmaverse martial artist would have to be travelling at roughly Mach 3.7 to have the same kind of energy. They still wouldn't have the momentum. To get that our theoretical 150 kg Martial Artist would be travelling at better then twice escape velocity for Earth. Ergo he wouldn't be able even stay on the planet.
...Fog, you wouldn't happen to know a guy named arkhangelsk by any chance, would you?
On topic: What would the TSAB do about Setsuna? It just seems that the magitech beurocracy would not like someone that isn't loyal to them or otherwise controllable to have that much power.
The Gates would probably be classified as a high-level but stable Lost Logia in need of immediate destruction/sealing to prevent the possibility of people traveling back into the timestreams of other universes and screwing things up with paradoxes and stuff. Setsuna may well be out of a job by the time the first season rolls around, assuming the bureau knows about the Gates at all.
While there would be a Death Phantom, it's history would be different as well.
DP would have a history for all of five minutes before he gets Befriended by Nanoha and/or Vivi--
....hold on a second. What if Crystal Tokyo becomes the new seat of the reformed Belkan Empire with Vivio (a few years down the line) in charge of things?
As for the Crystal Tokyo comments, I only really expect this story to go one SM season (After all, Nanoha's life after leaving junior high centers around her TSAB work on Midchilda, not her family in Japan, which takes her far away from the Senshi). If any prospective author can find a way to extend it to later seasons, though, I won't complain.
I don't think it would be too hard, it would just require some alterations to the StrikerS timeline. If Earth keeps being threatened by Chaos Spawn, then Nanoha will just keep coming back to put the smackdown on anything that looks at Earth the wrong way. First, though, we need to get through the first season before we can set up a definite sequence of events for later seasons.