Time to pay up!Bardic Inspiration is improved if it still recharges on a short rest after 5th level, which my bet is that it doesn't now.

From the WOTC article, it notes the new spell slot = BID is an accompaniment to the old feature, not an overwrite.
Font of Inspiration — Level 5
Font of Inspiration has always turned up the volume on Bardic Inspiration by restoring expended uses after completing a Short Rest in addition to a Long Rest. The 2024 Bard accompanies that with another additional way for Bards to recover expended Bardic Dice. Once you reach level 5, you can expend a spell slot to regain a use of Bardic Inspiration. This does not cost an action, so you can choose to use it when you want to expend the Bardic Dice.