Well, among other problems with that idea: neither DC nor Maryland wants it and there is no mechanism to force Maryland to alter its borders against its will.
It is not a power grab to give the citizens of DC the same rights as other Americans, it is correcting an injustice. If your concern is about DC then having too much power, I'd encourage you to look at the actual plan which preserves a core federal district that includes Congress and the Mall.
How noble, selfless, righteous and pure, for the political party which has just taken power with the narrowest of margins to suddenly take interest in "correcting an injustice" in a manner that secures additional power! Puerto Rico statehood will certainly be next; then, perhaps we can demand justice for cities like, say, Austin, on the premise that their citizens' representation is diluted by sharing senators with the rest of Texas.
How selfish and ignoble is it to oppose DC rights merely because they might benefit a political party you oppose?
There is nothing suspicious about the timing. DC has been fighting for statehood in earnest since the 1800s. There was a huge push in the 60s culminating in the 23rd Amendment, which for the first time allowed DC residents to vote for President. This was considered a matter of fairness and was broadly supported by both parties.
The slippery slope argument about Austin is ridiculous.
The state is named Maryland; it's called "retrocession." It already happened before, with the Virginia side of DC.
What? This is no good? Well, some people prefer the naked power-grab version, I suppose.