Is this likely to be practical in any way? Stratified is incompatible with other faction unity bonuses and likely isn't worth it, but a Decent Conditions Resident ruler is producing 6.5x the normal faction unity - in parlimentary system that's anywhere from 4.55 unity per pop to 6.5 unity per pop, depending on how egalitarian you are.
Yes, even without the exploit territory.
Faction Unity builds are actually surprisingly useful in the early game, when most players are getting most of their unity from rulers and dedicating their pops to workers, science, and alloys to get their initial defenses up. Being able to get a substantial amount of unity that doesn't require a job commitment- easily 2000+ in the first decade via early factions with Parliamentary Democracy + Fanatic Egalitarian, and is easily 1.6-1.9 times the faction unity from citizen pops. This is not just more traditions, but earlier traditions, which is good for getting key parts of your build set up sooner. Functionally, this can easily allow both a starting econ tradition
and Supremacy within the first two decades or so without a major sacrifice of your early military tech game. This is very useful for egalitarian war builds for year 20-ish wars, which- if successful- give yet more unity-producing pops, even as Egalitarians have an edict very good for converting them to your dominant ethic spread, and thus pressing them to both your worker economy and unity economy.
Separately, Residency as a citizenship status is actually stronger than many appreciate.
Residents have a -10% happiness, -50% political weight, but most importantly a -25% amenity upkeep requirement. While the happiness penalty is a stability debuff, the amenity requirement is a stability buff via making it easier to have excess amenities that increase happiness. (1.5x amenities required is +10% happiness.) You can also offset the 10% with the benefits of living standards. While this is always 10% less happiness than a citizen, the most important impact of pop happiness is the impact on state ethics cohesion. As long as happiness is above 50%, and amenities are positive, you're generally having higher pull to your state ethics than divergence.
A reason -25% amenity reduction is really useful, though, is that it can easily make gene clinics as viable for first 25 pop amenities as entertainers are for pure citizens. Basic coloniy buildings/2 rulers provide 11 amenities. At 80% habitability, 25 citizens need 30 amenities, or 19 from amenity jobs, the usual basis of 2 entertainers rather than 2 gene clinic healthcare workers and 1 entertainer. 25 residents need a bit under 24 amenities, or 13 from amenity jobs. 1 luxury housing (1000 minerals, 4 energy upkeep) covers the gap, letting 2 gene clinic workers- with their growth rate buff and job output buff- be as effective as 2 entertainers for citizens.
The main drawbacks of Residency is faction considerations. Residents cause a significant bias towards the Xenophile and Egalitarian factions, which isn't always desirable, and the decrease in faction unity per pop. Between less unity per pop, and a less stable ethics attraction situation (lower happiness, xenophile pull), it can be harder to keep your faction plan stable.
Unless, of course, what we've uncovered here.
The exploit for both of best worlds will be Fanatic Egalitarian-Materialist, where the bonuses come from the official ethics, but the benefits come from xenophile-ethics attraction and materialist living standards.
The goal here will be that you use your full citizen pops (and robots) as your worker base, where their full citizenship/no-citizenship faction unity is unchanged, while setting up your alien pops as resident researchers under Academic Privilage. Academic Privilage is +10 happiness for specialists (negating the happiness penalty), +10% research (equivalent to Intelligent for any RNG species), and +400% political weight (the exploit enhancing faction unity). If you set up a trade build and Merchant Spam, you can even spam 900% Merchants who, even if not thrifty, will produce substantial unity based on the exploit.
The fact that Xenophile will almost certainly be an overwhelming faction attraction is a feature, not a bug. It's not a state ethic, so pop unhappiness can go there, especially with the extremely high Xenophile ethic attraction of free xenos. However, as Egalitarian and Materialist you have no core disputes with the Xenophile faction, and it's trivial to keep them at 100% faction approval.
The core of the build will probably be using an aggressive early-war build (focusing techs on military, bypassing robots early on), using your first decade extra unity to race through Supremacy as well as an econ tradition to help afford the corvette fleets to conquer. Then you use your Egalitarian Encourage Political Thought edict to convert the captured homeworld of residents into unity-producing specialists/scientists to catch up on the econ science you bypassed for the war rush, and put your war-infrastructure towards CG and bloom with robots from a stronger position.