Harmonix has been talking about adding new features to Rock Band 4 even before it launched, and during their PAX East panel they unveiled some of their plans.
One of the most noteworthy announcements is that we'll be getting online multiplayer for free this holiday. That's all the wanted to say about it right now, but we'll get more information during E3.
But we won't have to wait that long, as they also detailed what to expect the coming months:
• May: Double kick pedal support and Battleborn characters.
• June: Practice Mode
• Fall: Expansion pack, enhancements to the Music Library (Filtering, hiding songs, ratings and more) and ION Drum support for the Xbox One.