<p>I am posting this answer mainly to try to kindle some further discussion.</p>

<p>As I wrote above, after posting my question (that you link to) I went through all PCA questions and retagged all kernel PCA ones to [kernel-trick]. But I did not touch kernel SVM questions. I think that manual retagging all such machine learning questions to [kernel-trick] would be a good thing to do, and if you are up to it -- go ahead.</p>

<p>(This will have an added benefit that you will be able to use this opportunity to edit, close, or answer some of the questions you go through.)</p>

<p>The more difficult question is what to do with the remaining questions, and here I am not sure. I agree with @gung that [kernel-regression] can be removed. Leaving [kernel] tag intact will make people use it instead of [kernel-trick], as it is currently happening every now and then. So I think the best course of action would be to merge [kernel], [kernel-density-estimate]=[kde], and [kernel-smoothing] into one tag that starts with [kernel-...].</p>

<p>I guess [kernel-density-estimate] might be the best candidate, but I am not sure.  </p>

<hr>

<p>Here are some possibilities:  </p>

<ul>
<li><a href="https://stats.stackexchange.com/questions/tagged/kernel-smoothing" class="post-tag" title="show questions tagged &#39;kernel-smoothing&#39;" rel="tag">kernel-smoothing</a> $\rightarrow$ <a href="https://stats.stackexchange.com/questions/tagged/kernel-density-estimate" class="post-tag" title="show questions tagged &#39;kernel-density-estimate&#39;" rel="tag">kernel-density-estimate</a></li>
<li><a href="https://stats.stackexchange.com/questions/tagged/kde" class="post-tag" title="show questions tagged &#39;kde&#39;" rel="tag">kde</a> $\qquad\qquad\rightarrow$ <a href="https://stats.stackexchange.com/questions/tagged/kernel-density-estimate" class="post-tag" title="show questions tagged &#39;kernel-density-estimate&#39;" rel="tag">kernel-density-estimate</a></li>
<li><p><a href="https://stats.stackexchange.com/questions/tagged/kernel-regression" class="post-tag" title="show questions tagged &#39;kernel-regression&#39;" rel="tag">kernel-regression</a> $\rightarrow$ <a href="https://stats.stackexchange.com/questions/tagged/kernel-density-estimate" class="post-tag" title="show questions tagged &#39;kernel-density-estimate&#39;" rel="tag">kernel-density-estimate</a></p></li>
<li><p><a href="https://stats.stackexchange.com/questions/tagged/kernel" class="post-tag" title="show questions tagged &#39;kernel&#39;" rel="tag">kernel</a> $\qquad\quad\, \rightarrow$ <a href="https://stats.stackexchange.com/questions/tagged/kernel-trick" class="post-tag" title="show questions tagged &#39;kernel-trick&#39;" rel="tag">kernel-trick</a>?</p></li>
</ul>
