Project 2 Task 1 (and it's descendants) will SHOW under Project 1 even though it may ultimately "live" under >>>Project 2. The link is, in effect, a virtual "doorway" to the other location. This does not violate the integrity of the tree structure in any way and, as I've said, tree structures like Linux's EXT3, EXT4, Mac's HPFS, Windows' NTFS, as well as ZFS, BTRFS, and other high performance file systems have done this for literally DECADES. This is not uncharted territory.
There are multiple use cases where I've wanted/needed this functionality. Contexts are not a substitute as there are times that something belongs in the tree in multiple places, not just "presented" that way in a flat viewport. This is usually a project planning or overview situation but I've encountered it in other places.
Another simplified example might be a shopping destination that exists both in your work and home tree structs. I can go to Home Depot for either reason. I don't want two separate "Home Depot" nodes (with their associated contexts, etc.) to live in two places. I want "Home Depot" avail in two places so I can list my work stuff here and my home stuff there. Yes, I will use a view based on Contexts for actually SHOPPING but for PLANNING, I want HD in two places in the tree.