Cyborg Korvac was able to slurp-up knowledge from Galactus' World-Ship with a Badoon computer counsel. He evolved himself into a Skyfather-tier cosmic entity with unlimited potential.
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Not convinced the Borg couldn't assimilate the cosmic tech and knowledge, especially with the Q spoon-feeding them.
It seems to be a staple of the Marvel Universe that this kind of evolution/ascension is possible under the right conditions. It happens often enough. The Borg should be able to cosmically upgrade just fine, especially with Q assistance.