http://www.edrdg.org/wiki/index.php/Editorial_policy#Is_it_worth_including.3F
https://www.investopedia.com/terms/1/51-attack.asp

This may be an ephemeral term, and fade from use in a year or so. Most dictionaries try and avoid ephemera.
OTOH an electronic dictionary is less troubled in this area. The marginal publishing cost for an entry is virtually zero, and while "clutter" can still occur, it's less of a problem.
If I encountered ５１％攻撃 I'd have to dig a bit to find out what it meant. I rather like having access to an immediate entry.

@@ -5,0 +6,3 @@
+</k_ele>
+<k_ele>
+<keb>５１パーセント攻撃</keb>
@@ -12 +15,2 @@
-<gloss>51% attack (on a cryptocurrency)</gloss>
+<gloss>51% attack (e.g. on a cryptocurrency)</gloss>
+<gloss g_type="expl">disruptive attack on a blockchain by majority holders of computing power</gloss>

I don't really agree with making a qualitative assessment of a term as "overly specialized", despite it getting plenty of hits on twitter 
etc. and also being used in mainstream media.

https://openledger.info/the-cryptocurrency-dictionary/

What I meant by the first half of my comment is that this term is perhaps too specialised.
We have a lot of technical terms in jmdict but they typically come from well-established fields/areas of study.
Of the many cryptocurrency terms that exist (see link above), only a few are worth adding to a general-purpose dictionary. I'd argue this isn't one of them.

I really don't see a difference between "this sort of thing" and something like 十五パーセントルール, 五十パーセント致死量, etc., all in daijs.

I'm not sure this sort of thing belongs in a dictionary. Not even Wiktionary has it. I also note that we don't have any other entries that contain the percentage sign.