Maybe this is just blind optimism, but the information coming directly from the city really did seem to support the idea that flexposts would be replaced with nicer, permanent barriers. Nothing has been explicit (or even implicit IMO) about removing any bike lanes. The aesthetics of old flexposts does genuinely seem to be a key issue here, and I can't say I disagree. Even when they're not hit by cars, they do become discolored and grimy quite quickly. The North Beacon St bike lanes have been in for less than 6 months and the flexposts are in pretty rough shape. Getting these replaced by concrete barriers and/or planters would look a whole lot better.
Regardless of the end result here, it is disappointing that the flexposts are being removed before a replacement is being installed (or even any plan communicated). Leaving the lanes unprotected, even if only for a few days or weeks, puts cyclists at risk. I fully expected BTD and this administration to do better, and hope they do in the future.
For more context, here's the initial Streetsblog
article on the Boylston Street bus lane removal, which also included info on bus/bike lane changes (emphasis mine):