When Google built their alternative to Perforce it wasn't possible for a team of seven to build a new system from scratch and port the entire company over to it in five months.
You can write it, but can you maintain it? Can you even fully understand what was built? Can you staff the team to manage the bugs? The potential data loss?
I'd wager it's still not possible.
You can write it, but can you maintain it? Can you even fully understand what was built? Can you staff the team to manage the bugs? The potential data loss?