Never did get into DOS editor : always seemed a bit too high of a learning curve.

I do have some experience with modding/mapping though, primarily using the StarCraft 2 editor. That thing is great - if your editor is half as good as it is, then you will have done a spectacular job. If you don't have anyone familiar with it, it might be a good idea to have someone spend a few days fiddling with it (or just watch some tutorials to see how easy it is to accomplish major overhauls) in order to understand all the features it offers, and how powerful it actually is. In particular, how the editor can be used to create fully custom abilities, effects, import models, or even create a new UI, with a scripting system that fires on top of more standard data editing.

That said, some things I would like to see (that the SCII editor does!) include :

Ability to make your mod depend on another - this will inherit any data changes made in the base mod, which you can then further modify.
When you start a new mod, it automatically sets up all the basic systems you need (I heard in DOS editor, you need to copy/paste and then fix scripts and such to even run a blank custom map, nevermind adding in campaign-like features).
A basic WYSIWYG first level editor : This allows you to create terrain (both fully custom and with prefabs), place units and features, and perform other basic operations. Clicking on units/features should allow you to do some basic customization of them (facing, unit level, feature size, etc)
A middling (XML-like) editor. This would be used to modify units (statistics, buffs, abilities), change or create abilities/items/crafting, add quests, etc. All fields have mouseover text explaining what they do.
A middling effects editor. This should allow you to view models or graphical effects, make a (limited) set of changes to them, such as scaling, rotation, recoloring, retexturing, etc, and give you options on when to use these new graphical effects (eg create a ice sparkle effect by recoloring, slowing the rain effect. This effect can then be used when a new snowfall ability is triggered)
An advanced scripting editor. This should take in arguments from the XML editor (eg if you create a new ability in the XML, you should be able to trigger something to happen when it is used, or if you need a more complex quest chain, you could make one here)
Ability to import custom models, icons, etc would be wonderful.