There’s a big conceptual difference between God being essentially love, and God only doing love. A lot of trinitarians inadvertently (and against our own theology) reduce God’s love down to the level of God’s wrath (or worse, put God’s wrath on the level of God’s love as though God is essentially wrath – they may say God is essentially justice, but the way they go about it means only that God is also essentially wrath).
So, not being essentially wrath at the level of His own self-existence, God can choose to do wrath to some creature, and to stop doing wrath to some creature, and to always do wrath to some creature, and to never do wrath to some creature. If God is not essentially love, God could choose to do love to some creature, and to stop doing love etc. Love is as optional for God as wrath, it’s only a question of whether He does it or not. And He might change His mind later.
Non-trinitarians try to get around this by claiming God can still be essentially love on their theologies, but the closest I’ve ever seen someone actually get to that, is the idea that God’s self-existence necessarily requires loving some equally eternal not-God creation; and that isn’t even supernaturalistic theism any more. (Both God and not-God exist distinctly within a shared overarching reality that is neither God nor not-God!) Otherwise the claims I’ve seen along this line amount to some static assertion, or amount to some feeling God happens to always have, or reduces back to God merely choosing to love whatever He creates and maybe to love only Himself in what amounts to selfishness if there was no creation. None of that is the same as God being essentially love in God’s own self-existence.
However, universal salvation could still be possible under any of those ideas. And I think a solid scriptural argument could be made apart from the metaphysics of the question, which would work just as well for a unitarian Christianity (maybe also for a modalistic one, depending on what scriptures are used), to the effect that God reveals His intentions to save all sinners and also reveals He shall surely accomplish those intentions.
If for example we accept Peter as being sufficiently inspired for this kind of data, and if we accept the Petrine epistles as coming legitimately from Peter, and if Peter says there that God has makrothumia toward all sinners, and shortly afterward in the same context warns that we had better regard God’s makrothumia as salvation (i.e. as an assurance of salvation) on pain of being false teachers, then we don’t have to bring in questions of Christology and/or Pneumatology. Modalist, unitarian, and bi-or-trinitarian Christians could all in principle agree to what the revelational math about salvation adds up to there, and so agree that however else we interpret Peter’s strong warnings of coming punishment to false teachers in those same epistles (and in Jude’s related one) we ought not to interpret them so as to falsify either of those gospel assurances on pain of being false teachers ourselves.