A release date for the Season 4 DVD has been set in the UK. Thanks to @WorbsE17 for spotting that the DVD (region 2) will be available there as of September 25th. Amazon UK is taking pre-orders for £27.99. No date has been set for the US as of yet.

According to the BBFC, it looks like a fan favorite - the Gag Reel - may not be included this time around. What does appear to be included are 14 minutes of Deleted Scenes. They are detailed on the site as follows:

00:00:49:24  EP 402 SC 10
00:00:48:18  EP 403 SC A28
00:02:10:15  EP 404 SC 1 - PARTIAL
00:00:41:13  EP 406 SC 11 PT 1
00:00:33:04  EP 406 SC 11 PT 2
00:00:48:03  EP 406 SC 39
00:00:28:03  EP 409 SC 20
00:00:15:12  EP 409 SC 11
00:00:53:18  EP 410 SC 19
00:00:22:20  EP 410 SC 19
00:00:28:01  EP 411 SC 29
00:01:44:18  EP 412 SC 05 - EXTENDED
00:01:25:12  EP 412 SC 40 - EXTENDED
00:02:41:01  EP 413 SC 10
00:00:07:05  EP 413 SC A 28
 

As soon as a US release date is announced, it will be posted here.

UPDATE: Thanks to @marisaroffman, we now know that the Sleepy Hollow Season 4 DVD will be released in the US on September 26th. Even better, a complete 4 season set will be released on that day as well.