Some numbers: there are ~120kloc of Elisp in Emacs proper. I have nearly 500kloc of Elisp in my `.emacs.d`. Granted, some of it are reimplementations and wrappers around what is in the core, and some are plugins I downloaded, tried out and forgot to delete, but still, that's a huge amount of code. That's 136 man-years, according to sloccount:

    Total Physical Source Lines of Code (SLOC)                = 499,088
    Development Effort Estimate, Person-Years (Person-Months) = 136.18 (1,634.17)
     (Basic COCOMO model, Person-Months = 2.4 * (KSLOC**1.05))
    Schedule Estimate, Years (Months)                         = 3.47 (41.59)
     (Basic COCOMO model, Months = 2.5 * (person-months**0.38))
    Estimated Average Number of Developers (Effort/Schedule)  = 39.29
    Total Estimated Cost to Develop                           = $ 18,396,178
     (average salary = $56,286/year, overhead = 2.40).
    SLOCCount, Copyright (C) 2001-2004 David A. Wheeler

>As an answer to sibling comments: if your Emacs clone doesn't support elisp, then it's not a replacement because the elisp code out there is the #1 selling point of Emacs.

For some. For others a clone that does 20% of what Emacs does and has a few nice plugins could be enough.