I respect your choices and agree on Acapella and Proac. Just an observation. Your list reads more like a My Best list rather a most significant. That's ok. While you don't like panels, it looks like we both shy away from boxes.
P.S. I think horns are a great choice for classical music.
It IS a "my best" list

I never had any intention of writing a "most significant speakers of all time" list, given my inexperience with many speakers found on many lists. Here is a selection of lists:
The Absolute Sound: Quad ESL-57, Acoustic Research AR3a, Rogers LS3/5a, Wilson WATT, Magico Mini II, Dahlquist DQ-10, Magnepan 1-U/1-D, Infinity IRS V, KLH Model 9, Advent, MBL 101e, Klipschorn. From this list I have only heard the Quads, Rogers, Wilsons, Magico, and MBL. And the only speaker I rate from those I have heard on that list are the MBL's.
Audioholics: Acoustic Research AR1-7, Advents, Bose Acoustimass AM-5, Bose 901, KLH Six, Seventeen, and Five, Klipschorn, JBL L100, B&W 800 series, Magnepan Magneplanar, Thiel 3.6. I have heard the B&W's, both Bose systems and the Thiel. I rate the Thiel as a good speaker, but wouldn't say I was wowed by it.
CNET: Hansen Audio Prince V2, Naim Ovator S-600, Gallo Acoustics Reference 3.5, B&W 802D, Wilson MAXX, JBL Synthesis 1400, Magnepan 20.1, Vandersteen Model 7, Martin-Logan CLX, Focal Grande Utopia EM. I have heard the Gallo, 802D, and CLX. You have to wonder what the writer was smoking to mention the Gallo in the same article as the awesome Martin-Logan CLX.
Many of the speakers on these lists were never marketed in Australia, or if they were, never achieved enough commercial success for me to be lucky enough to be invited to someone's home for a listen. I have no idea if Klipschorns deserve to be on that list or not, given that I have only read about them, much less seen one in real life or heard one.
There are many ways to define "significant" ... you might mean commercially successful (in which case you should be including Sonos), or technologically innovative (then it would be fair to include the Quad ESL's, and we have to ask ourselves if we should include Google Home), or the best engineered, or the most expensive ... the list goes on. Perhaps we should start by what we mean by "most significant".