I suggest filing a feature request. Combining those widgets sounds like a good idea. If you are more of an adventurous type, you could even implement it yourself, and share it in the App Store :)
You can use an XPath constraint to achieve the same.
Implementing a datasource microflow as a property of the widget may be an option because you can retrieve references by association in microflow and simulate the constrained by behaviour.
But that will be tricky because you can't send primitives (the String search value) to microflows. But in 4.x maybe a combination with non persistent objects can be the solution. Would be a nice addition to the widget.