A couple of things.
There's no way an increase to even to just 28% will get through a Republican House and a Republican Senate while Obama is in office. In that sense, this is the move of a master politician. He's advocating a change that would be in the public interest and which will certainly appeal to the working/middle class, and which the Republicans almost certainly won't go along with.
If they do as expected and vote against a capital gains increase, Obama can blame the Republicans and the Democratic Party can use it to make the Republicans look like they don't care about the the working and middle class (they don't particularly, but the Democrats aren't exactly MLK either). If they come out nowhere and actually agree to a 28% capital gains rate, Obama gains legacy points while the Republicans don't lose points with the majority of the public on this issue.
All of this said, I think the best move would be to come at the tax code for a serious overhaul. It's way too long, convoluted, and riddle with loopholes. The tax brackets could be much simpler and should be much more progressive.
The economists Saez and Piketty suggest that the top marginal tax rate should be in the ballpark of 80%. Here's how I'd shift the brackets for a single person filing with no dependents:
First, add income and capital gains together.
Nothing at all is taxed until you've reached $25K.
Marginal income/capital gains between $25K and $100K is taxed at 25%. So somebody making $50K is effectively taxed at a 12.5% rate and somebody making $100 is effectively taxed at an 18.75% rate.
Marginal income/capital gains between $100K and $400K is taxed at a 50% rate. So somebody making $400K in a year is getting an effective tax rate of about 42.19%.
Marginal income/capital gains above $400K are taxed at a rate of 75%.
Tether it all to inflation.