According to an announcement post on the www.tenforums.com  The delayed Spring Creators Upgrade is to be available, Monday, April 30. 
 
https://www.tenforums.com...monday-april-30-a.html
 
 

Do we have to accept it? What a load of hooey crap to bog my pc down even more with unwanted apps and privacy intrusions from what I see. I could be wrong, some people may love it...
 
But thanks for the link, looks like a lot of good info there!

According to google search (windows central.com):
 
Similar to previous rollouts, Microsoft will be releasing the Windows 10 April Update slowly and on stages. Starting on April 30, the company will be making the new feature update available for download manually, then on May 8, it'll be more broadly available through Windows Update for newer desktops, laptops, and tablets that have been tested to be compatible with the new feature update. These devices may include Surface and branded PCs (such as those from HP, DELL, Lenovo, ASUS, Acer, etc.) that came pre-installed with Windows 10.

The 1803 is live.  I got it and although I haven't gone into depth with CbB, initial tests show 1803 had no affect.   
 
However, I already had it with the Windows Insider program version and I didn't encounter any problems running Sonar/CbB.

I've just installed it on most of my PC's... and would you believe it, I got a 1 min power cut right in the middle of upgrading one of them. I was raging! Thankfully, it recovered gracefully.
 
However... the usual upgrade fallout:

• XLN Audio (Addictive Drums 2) needed re-authorising, as it thinks it's a different PC
• My Scarlett 6i6 wasn't recognised and needed it's drivers re-installed
• My registry entries for mapping my samples drive to a directory got removed, and needed re-adding.

Once those issues were sorted, everything appears to be working fine.
 
M.