You can measure the influence of a designer in multiple ways, and Tresham's legacy might be best represented by his influence on other game designers, specifically his creation of two game genres — 18xx games and civilization games — through the publication of the stock-manipulation and rail-building game 1829 by his own Hartland Trefoil Ltd. in 1974 and Civilization (also by Hartland Trefoil) in 1980.
I wish that I could say more than that, but I've played 1830 once and Civilization never as they're not my style of games. Instead, I can only recognize how Tresham's work has inspired others, both those who have created games of their own in these genres and those who play these games with a passionate devotion, such as Edward Uhler of Heavy Cardboard, who interviewed Tresham in mid-2018:
• On November 14, 2019, Kai Jensen noted on BGG that her husband Chad Jensen, designer of Dominant Species and the Combat Commander series of games, had passed away. Jensen had been diagnosed with cancer earlier in 2019, with BGG user Christopher Hill posting a warm tribute to the designer at the time.
• Baltic publisher Brain Games has entered a distribution agreement with Canadian publisher/distributor Luma Games, with Luma now having "exclusive English-language distribution" of its titles in the United States, Canada, Australia, and New Zealand. On top of that, Luma Games will "manage Brain Games's French catalog for Canada's French language market".
In June 2019, Luma had picked up distribution rights for Italian publisher Horrible Games — which changed its name to Horrible Guild in October 2019 — in North America. Luma also recently announced that it will be demoing and selling Bruxelles 1897 at BGG.CON 2019 on behalf of Belgian publisher Geek Attitude Games, with that title moving into North American distribution in early 2020.
• German publisher Pegasus Spiele has signed a deal with Canadian distributor Lion Rampant Imports to give that latter company exclusive distribution of Pegasus titles in Canada. (In case you forgot or missed the news, Asmodee had signed a deal in August 2019 to purchase Lion Rampant Imports.)
• Along the same lines, in mid-October 2019 Pegasus signed a deal with Let's Play Games Distribution and VR Distribution to give these two companies exclusive distribution rights of its titles in Australia, and in early October 2019, Pegasus signed a deal with Spilbræt.dk for exclusive distribution of its titles in Denmark, Sweden, Norway, and Finland.