I'd be rather disappointed about 2TB and 3TB Time Capsule models.
I'd much prefer a smaller Time Capsule with a 2.5" drive.
Benefits would be: It could be smaller, consume even less power and run quieter, cooler and more reliable.
1 TB capacity is enough for most people.
Actually, it's way more than enough.
We sell multiple 1 TB ones for every 2 TB one.
Few home users I know need more than 1 TB of storage. Even if you have that much data or more, it would take forever to send over Wi-Fi. And if you really
need more than 1 TB of storage (let's say you are a system administrator or creative professional), you better not entrust your important data to a lowly Time Capsule.
Current Time Capsules do not lack in terms storage capacity or ease of use. Not even functionality paired with a Mac. They lack in terms of
1) price point. Many people shy away from buying one just because of their price point - and then some end up doing no data backup at all, cause they too are lazy to use a tethered drive just for backup purposes.
2) backing up non-PC devices. iPhones, iPads, iPod touches. Because, again, many are too lazy or stupid to regularly hook them up to a PC. If they even own one. Many don't even have an internet connection besides their iPad / iPod wireless plan. Syncing their oh-so-important photos, apps and videos to iCloud or somewhere else could eat up the biggest part of their monthly data allowance or more - so I can definitely see demand for local backup in addition to or instead of iCloud.