I'm with Watto here. For those that are not aware, broom style is a formal upright style for deciduous trees. To be considered broom the trunk should be vertical and straight. Nebari is important and branches flow up and out to create an umbrella canopy.
That's broom style. It has a pretty strict definition however you can grow a tree in any shape you want. If you want a tree with an umbrella canopy and a bent trunk then you are entitled to do it. Just don't call it broom style.
Traditionally zelkova was almost always grown as broom style because that's the natural shape of this species. I notice that there are more Japanese zelkova bonsai that are not broom style. Younger, innovative bonsai artists are challenging the accepted codes of traditional bonsai in many aspects, including what styles suit zelkova.
FWIW I would not make radical trunk chops just to straighten this trunk. Not only is it a waste of material, there's also a good chance it may not work out as expected.
I would be happy to develop this as an informal upright but with rising zelkova like branches - sort of a cross between broom and informal upright. If the traditionalists want to challenge the validity of the style
Trunks also tend to straighten as they thicken. They grow faster on insides of curves and slower on the outsides so as this one develops some of that curve may even disappear. Who knows, in future it may even get straight enough to fit into traditional broom style parameters.