They existed in the SVG 1.1 spec [1], but were removed from SVG2 [2] (although not mentioned in the "changes" chapter it seems - problably missed because of the SVGLocatable/SVGTransformable merge.)

[1] https://www.w3.org/TR/SVG11/types.html#InterfaceSVGLocatable
[2] https://www.w3.org/2015/02/11-svg-minutes.html contains the resolution

Spec bug filed at: https://github.com/w3c/svgwg/issues/309

Counters for these:

https://www.chromestatus.com/metrics/feature/timeline/popularity/204
https://www.chromestatus.com/metrics/feature/timeline/popularity/205

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b0b7464ec0a5ad96eff09508eafdc3d0950a1617

commit b0b7464ec0a5ad96eff09508eafdc3d0950a1617
Author: fs <fs@opera.com>
Date: Sun Feb 26 20:49:56 2017

Add comment about SVGGraphicsElement.{nearest,farthest}ViewportElement

Move to bottom of interface per common practice.

BUG=695981

Review-Url: https://codereview.chromium.org/2714123003
Cr-Commit-Position: refs/heads/master@{#453124}

[modify] https://crrev.com/b0b7464ec0a5ad96eff09508eafdc3d0950a1617/third_party/WebKit/Source/core/svg/SVGGraphicsElement.idl

These were removed based on usage counters giving very low values, and there being a pretty simple way to implement this functionality if it's needed by authors.

There's some discussion here:
https://www.w3.org/2013/11/14-svg-minutes.html#item12
https://www.w3.org/2015/02/11-svg-minutes.html#item12

https://github.com/w3c/svgwg/issues/309#issuecomment-283181634