In the Interactive Diagrams I inserted as main diagram in existing articles I always respected the design choice of the author, trying to make the Interactive Diagram resemble it as closely as possible.
That is usually appropriate, especially when the author is still active on the site.
Should there be a systematic effort to eliminate all piece representations other than Alfaerie?
No, but it's usually appropriate to replace Utrecht with Alfaerie. The Utrecht style was frequently used on pages, because it got a head start on other sets. It was created by the site's founder, and he created some JavaScript code for displaying diagrams on pages. Since then, David Howe and I produced some better looking sets out of Chess fonts. David's Alfaerie set became particularly popular, and many people added new pieces to it. When I make a diagram, I choose the most suitable set for that game. This is sometimes Alfaerie, and it is sometimes not, but it is never Utrecht.
That is usually appropriate, especially when the author is still active on the site.
No, but it's usually appropriate to replace Utrecht with Alfaerie. The Utrecht style was frequently used on pages, because it got a head start on other sets. It was created by the site's founder, and he created some JavaScript code for displaying diagrams on pages. Since then, David Howe and I produced some better looking sets out of Chess fonts. David's Alfaerie set became particularly popular, and many people added new pieces to it. When I make a diagram, I choose the most suitable set for that game. This is sometimes Alfaerie, and it is sometimes not, but it is never Utrecht.