Pronunciation of letters "g" and "c" in blend words
Solution 1:
There is no "should" or prescriptive rule for pronunciation of unfamiliar words. What people do which resembles a rule is to apply common patterns, such as soft g before e, when a new word comes along.
As this new word circulates, you are likely to hear a lot of “rEH-jeks”, following the common pattern, but also a lot of “rEGG-ex”, after the word “rEGG-u-lar”. And eventually one will win the day. We'll just have to wait to see how it turns out.