In general, it is quite feasible to design an XML format which defines the model to be represented by XSD in a very compact and readable way - resembling closely the instance documents described by the XSD - and generate the XSD from such "XSD design" documents. A simple example:

<x:xsdd xmlns:x="http://www.xsdr.org/ns/xsdd" ...>

    <x:stypes>

        <x:stype name="LocaleOrLangType" typeDesc="#[a-z]{2}(-[A-Z]{2})?#"/>

        ...

    </x:stypes>

    <TravelAgenciesRQ>
        <RQ_Metadata Language="$LocaleOrLangType" RequestID="xs:string" TransactionID="xs:string"
            >#empty</RQ_Metadata>
        <TravelAgencyFilter x:occ="?">
            <x:_choice_>
                <TravelAgencyIDs>
                    <TravelAgencyID x:occ="+">$NonEmptyString32</TravelAgencyID>
                </TravelAgencyIDs>
                <TravelAgencyShortNames>
                    <TravelAgencyShortName x:occ="+">$NonEmptyString</TravelAgencyShortName>
                </TravelAgencyShortNames>
            </x:_choice_>
        </TravelAgencyFilter>
    </TravelAgenciesRQ>

In fact, as a rule I do not write XSDs any more, but write xsdd (XSD design) documents instead.