I'm a big fan of Trey and his story, even before last season, was a good one. Never really a top prospect, earned his way into the lineup, took advantage of opportunity playing OF or whatever to stick around.
My preference would be to extend him for a number of reasons, but this isn't really about what I'd do.
Last season created a challenge where you really need to see him back in an Oriole uniform and he's accomplished that in spades. He'll continue to get his timing and produce good or better numbers. If he is anything around an .800 OPS this year he likely gets something in the 7M range in arbitration.
My guess is that's not going to work for the Orioles and puts them in the uncomfortable box of having to trade him. The can't non-tender him (that would be wildly outraged) and if you wait to trade him in the offseason and it's apparent you're trading him, you can't even leverage value.
The best option is to trade him sooner than later. You save the most money and if you can find some need today, maybe you can leverage some in-season value.
We've already seen the Oriole beat writers float this trial balloon and that's likely pretty intentional on their part. Most people are pretty accepting of a trade consideration, you do it under the mantra of continuing to build pieces and make the easy argument that pushing Trey into a playoff race is good for him too.
The question becomes when, who and for what more than if.
WHERE: I always start with need and HERE is the current MLB 1B by OPS. Kind of funny from the Mountcastle discussion, but most of the bottom of the list is the better teams. Not all of them would be in the market for help.
WHEN: well, it's before the trade deadline, but I'd argue that earlier might be better. 'Get a good look at some other players that may contribute to the future' and 'let Mountcastle run at 1B for the rest of the season'. Ultimately, the earlier you move him, the better off the Orioles would be from the optics (get it over with) and cost (sooner is more savings) angles.
WHAT: People may want a big haul, but RHed 1B with a year+ of service aren't really the 'give up the farm' type deals.