Blesta won't replace WHMCS. Sorry to burst your bubble, but it's just not happening. Here's quite a few reasons why:
#1 : WHMCS is backed by cPanel. This is no small feat, and these giants won't just let their investment go.
#2: WHMCS is actively developed. When was the last time we saw a major Blesta update? Almost 3 years ago. Yes, v3 has been out for that long. The last time we saw a major WHMCS update? March/April with 6.3
#3: WHMCS will have php7 support, likely before ioncube does.
#4: Did I mention they're not really actively developing Blesta? See http://www.blesta.com/forums/index.p...gateway-vault/
for a perfect example. Topic created September 2013. very, very valid gateway (Quantum vault) , yet where is it? They still haven't bothered to put it together.
#5: Extendability . You can do so much more with WHMCS than you can anything else.
Yes, I'm slightly biased. I've been working on WHMCS installs for years, but Blesta doesn't have a chance at 'replacing WHMCS'. As it sits right now, nothing does. Nothing out there has the power to take the beast that is WHMCS down. Trust me, I've tested almost all of 'em.
In time, someone will dethrone the king, always happens (anyone remember moldernbill ?), but typically, that's an upstart, someone just starting out. Nukern might stand a slight chance, but they need to get away from the whole 'cloud' idea. That's just scary as anything for billing software.