Graduating Wharton at 19 and having four years work experience at 23 as a strategy consultant should offset your GPA.
Overlooking that numerical anomaly - your GPA at Wharton certainly ain't going to help you get in anywhere. It is so directly applicable. A decent GMAT and story is really critical to turning this around.
Yeah, an MBA is a good way to switch to IB. Hundreds of people do it a year. No-one really gives two hoots about your GPA - for IB they will want to know how you did in Accounting and Finance.
Bulge Brackets hire people without experience after MBAs the same way as they do after college, and for the same reason. They need lambs to the slaughter to work long days drafting stuff for a high RoE. The attrition rate in IB is so high they need to bring in numbers.
I really don't get your analyst question about taking two years out. I think you probably want a better reason to do an MBA than simply to get into an IB. While it is often a means to similar ends, you kind of have to care about the education (with your UG GPA this would be a huge concern). While it isn't academic rocket science, it is a college and they care about the academic perception of the program.
If you can network into an IB go for it.
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