It's happened before, after all the first year 100% of the teams were rookies
The last time it was as high as 25% was in 2003, but you can see in the table below that 25% isn't extreme.
However, they are usually spread out, and Texas has already experienced what it's like to have a flood of rookies overwhelming the vets. I guess Texas is experienced with the inexperienced...
Year --- # Teams -- Vets --- New ---- % new teams
1992 ---------- 28 ---------- 0 ----------- 28 ---------- 100.0%
1993 ---------- 25 ---------- 14 ---------- 11 ---------- 44.0%
1994 ---------- 44 ---------- 22 ---------- 22 ---------- 50.0%
1995 ---------- 59 ---------- 30 ---------- 29 ---------- 49.2%
1996 ---------- 94 ---------- 48 ---------- 46 ---------- 48.9%
1997 ---------- 155 --------- 83 ---------- 72 ---------- 46.5%
1998 ---------- 199 --------- 137 --------- 62 ---------- 31.2%
1999 ---------- 269 --------- 166 --------- 103 --------- 38.3%
2000 ---------- 372 --------- 241 --------- 131 --------- 35.2%
2001 ---------- 515 --------- 333 --------- 182 --------- 35.3%
2002 ---------- 641 --------- 456 --------- 185 --------- 28.9%
2003 ---------- 787 --------- 590 --------- 197 --------- 25.0%
2004 ---------- 927 --------- 711 --------- 216 --------- 23.3%
2005 ---------- 988 --------- 805 --------- 184 --------- 18.6%
2006 ---------- 1133 -------- 901 --------- 233 --------- 20.6%
2007 ---------- 1301 -------- 1037 -------- 264 --------- 20.3%
2008 ---------- 1501 -------- 1187 -------- 317 --------- 21.1%
2009 ---------- 1677 -------- 1359 -------- 320 --------- 19.1%
2010 ---------- 1808 -------- 1531 -------- 277 --------- 15.3%