This article was inspired by this FanPost, which references a recent radio interview in Portland, Oregon which appeared to indicate that interest in having a MLB team in Portland was ramping up.
Most likely, a Portland team would come via expansion, not relocation, even though there was talk of relocation in the radio interview.
Expansion is likely coming to MLB. It’s probably at least five years away and very likely more.
When it does come, another team would likely be added so as to produce two 16-team leagues, broken down into four divisions of four teams each.