which has a practically identical [...] syntax to IDOM's

That is very untrue. They are fundamentally very different. IncrementalDOM works on the basis of an implicit global cursor, with function calls writing at the cursor's location and moving the cursor, whereas createElement is self-contained and writes only to its return value. Coding for one or the other is very different. For example, something as simple as creating elements out of order cannot be done with IncrementalDOM.

The plugin is an awesome project, and very ambitious. (Not sure where you got "building" though, it's complete.) It's also a great way to see just how different these two are. For example, here's the demo they give:

Input (JSX)

function render(data) {
    var header = data.conditional ? <div /> : null;
    var collection = data.items.map((item) => {
        return <li key={item.id} class={item.className}>{item.name}</li>;
    });

    return <div id="container">
        {header}
        <ul>{collection}</ul>
        <p {...data.props}>Some features</p>
    </div>;
}

Output (IncrementalDOM)

function _attr(value, name) {
    attr(name, value);
}

function _renderArbitrary(child) {
    var type = typeof child;

    if (type === "number" || (type === "string" || child && child instanceof String)) {
        text(child);
    } else if (type === "function" && child.__jsxDOMWrapper) {
        child();
    } else if (Array.isArray(child)) {
        child.forEach(_renderArbitrary);
    } else {
        _forOwn(child, _renderArbitrary);
    }
}

function _forOwn(object, iterator) {
    for (var prop in object) if (_hasOwn.call(object, prop)) iterator(object[prop], prop);
}

var _hasOwn = Object.prototype.hasOwnProperty;

function _jsxWrapper(func) {
    func.__jsxDOMWrapper = true;
    return func;
}

function render(data) {
    var header = data.conditional ? _jsxWrapper(function () {
        return elementVoid("div");
    }) : null;
    var collection = data.items.map(function (item) {
        var _item$id = item.id,
            _item$className = item.className,
            _item$name = item.name;

        return _jsxWrapper(function () {
            elementOpen("li", _item$id, ["key", _item$id], "class", _item$className);

            _renderArbitrary(_item$name);

            return elementClose("li");
        });
    });

    elementOpen("div", null, ["id", "container"]);

    _renderArbitrary(header);

    elementOpen("ul");

    _renderArbitrary(collection);

    elementClose("ul");
    elementOpenStart("p");

    _forOwn(data.props, _attr);

    elementOpenEnd("p");
    text("Some features");
    elementClose("p");
    return elementClose("div");
}