Re: inkscape featues
This is true, it can be added in the xml and Inkscape will then display it, unfortunately, very few programs that support svg will follow through with that and it does not correspond to underlined output when saved out to PDF or similar to send off to my print department.
As another professional who works with Inkscape, I'm pretty sure telling my clients that I've decided that they cannot have underlined text because it's "discouraged" would not go down well. I really do like using Inkscape however lacking something so basic is the painful reason we have to pay for corel draw "spit spit". Open source stuff often has the issue of people working on exciting features and code, no-one is made to do the dull stuff and so it sometimes gets left behind. I'm the same, I often help out with open source projects, I never take on the boring code!