Would never be added. Nothing against your idea, but look at the progression of defenses:
| 2 |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
| 2 |
1 |
25 |
- |
- |
- |
- |
- |
- |
- |
- |
| 2 |
1 |
50 |
1 |
- |
- |
- |
- |
- |
- |
- |
| 2 |
2 |
75 |
1 |
1 |
- |
- |
- |
- |
- |
- |
| 3 |
3 |
100 |
1 |
1 |
- |
1 |
- |
- |
- |
- |
| 3 |
3 |
125 |
2 |
1 |
1 |
2 |
- |
- |
- |
- |
| 5 |
4 |
175 |
3 |
2 |
1 |
2 |
- |
2 |
- |
- |
| 5 |
5 |
225 |
4 |
3 |
1 |
3 |
2 |
3 |
- |
- |
| 5 |
6 |
250 |
4 |
4 |
1 |
4 |
2 |
4 |
2 |
- |
| 6 |
7 |
250 |
4 |
4 |
1 |
4 |
3 |
4 |
3 |
2 |
This is all defenses, not including traps. (I left in the skeleton traps, since they have a health and have to be destroyed). Note how there is only 1 defense for each TH upgrade? In order for your idea to happen, it would be a TH11 idea, to keep with this trend. Quote frankly, it just wouldn't make much of a difference in that level raids.