In an interview with ABC News' Rebecca Jarvis about Apple's investments in the U.S. economy, CEO Tim Cook confirmed that an upcoming iOS developer beta, due to be released in February, will include, in addition to a previously announced battery health screen, a setting to disable iPhone performance throttling. Cook explained that, while Apple will recommend to keep throttling enabled to prevent unexpected shutdowns in emergency situations, iOS will also include an option to turn it off for users who don't want their iPhone's performance reduced by software.
As noted by Benjamin Mayo at 9to5Mac:
You can listen to Cook talk about this in the interview embedded below. Skip to around 4:30 to hear him talk about the iPhone slowdown debacle. His wording is not ambiguous, he states plainly that Apple will release the developer beta (presumably iOS 11.3) next month and that it will include the ability for users to disable performance throttling if they want to.
Given Cook's comments, it sounds likely that iOS 11.2.5 (currently in beta) will be released by the end of the month, with iOS 11.3 beta following in February and a possible launch in March, as with other .3 releases in previous years.