<div>
    <p>Good text</p>
    <blockquote>Good text</blockquote>
    Problematic text <strong>like this</strong> one.
    <p>Good text</p>
</div>

p {
    max-width: 300px;
    margin: 0 auto;
    padding: 10px;
}

jQuery("div").contents().filter(function() { return this.nodeType === 3; }).wrap('<p>');